Optical recording and reading method, optical recording and reading apparatus, optical recording medium, and method for producing an optical recording medium

ABSTRACT

An optical recording medium includes a recording and reading layer that is previously staked or formed afterward and has no concavo-convex pattern for tracking control, and a servo layer in which a concavo-convex pattern or a groove for tracking control is formed. Information can be recorded in the recording and reading layer while tracking is performed using the servo layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical recording medium including aplurality of recording and reading layers, an optical recording andreading method and an optical recording and reading apparatus thatrecord information on the optical recording medium, and a method forproducing the optical recording medium.

2. Description of the Related Art

Conventionally, optical recording media such as a CD-DA, a CD-ROM, aCD-R, a CD-RW, a DVD-ROM, a DVD-R, a DVD+/−RW, a DVD-RAM and a Blu-rayDisc (BD) have been widely used for viewing digital moving image contentor recording digital data. Among them, in the BD, which is regarded asone of next-generation DVD standards, a wavelength of laser light usedfor recording and reading is set to be short, that is, 405 nm, and anumerical aperture of an objective lens is set to 0.85. In an opticalrecording medium conforming to the BD standard, tracks are formed at apitch of 0.32 μm. In this way, data of 25 GB or more can berecorded/read on/from one recording and reading layer of the opticalrecording medium.

Incidentally, capacities of moving images and data are expected toincrease more and more in the future. Accordingly, there has beenconsidered a method for increasing a capacity of the optical recordingmedium by providing multiple recording and reading layers in the opticalrecording medium. For the optical recording medium according to the BDstandard, there has also been reported a technique for realizing anultra-high capacity of as much as 200 GB by providing six to eightrecording and reading layers (see I. Ichimura et. al., Appl. Opt, 45,1974-1803 (2006), and K. Mishima et. al., Proc. of SPIE, 6282, 62820I(2006)).

On the contrary, if the multiple recording and reading layers areprovided in the optical recording medium, formation of concavo-convexpatterns such as grooves/lands for tracking control on each recordingand reading layer leads to a complicated medium configuration, causingconcern about difficult eccentricity adjustment work and the like.Moreover, a stamper as a mother die for forming the concavo-convexpatterns is required for each provision of the recording and readinglayer. Thus, a larger number of layers increases the number of times ofuse of this stamper, and accordingly increases production costs.

Consequently, in recent years, there has been proposed a technique forseparately providing servo layers having concavo-convex patterns andgrooves, and recording and reading layers not having the concavo-convexpatterns and the grooves, in an optical recording medium, and recordinginformation on the recording and reading layers by using a beamdedicated to recording and reading, while obtaining tracking signalsfrom the servo layers by using a beam dedicated to tracking control (seeJapanese Patent Laid-Open Nos. 2008-97693 and 2008-97694).

More recently, there have been proposed techniques of a 20-layered ROMtype optical recording medium (see A. Mitsumori et. al., Jpn. J. Appl.Phys., 48, 03A055 (2009)), a 10 to 16-layered write-once opticalrecording medium (see T. Kikukawa et. al., Jpn. J. Appl. Phys., 49,08KF01 (2010), M. Inoue et. al., Proc. SPIE, 7730, 77300D (2010), and M.Ogasawara et. al., Tech. Dig. of International Symposium on OpticalMemory 2010, 224 (2010)), and the like. Use of an optical system (awavelength and a numerical aperture) similar to the BD standard hasbecome likely to be able to achieve a recording capacity on the order of500 GB.

Moreover, for the purpose of simultaneously reading two layers, therehas also been proposed a technique for alternately stacking recordinglayers having concavo-convex patterns and grooves, and recording layersnot having the concavo-convex patterns and the grooves (seeInternational Publication No. WO2008/099708).

However, according to the technique of International Publication No.WO2008/099708, an increase in the number of the recording and readinglayers causes the number of the recording layers having theconcavo-convex patterns and the grooves to increase, which, after all,leads to the complicated medium configuration, the difficulteccentricity adjustment work and the like.

Moreover, according to the techniques of Japanese Patent Laid-Open Nos.2008-97693 and 2008-97694, as the number of the recording and readinglayers increases, a distance between the recording and reading layer andthe servo layer increases, and thus a thickness tolerance can easilyoccur between both layers. Specifically, the recording and reading beamapplied to the recording and reading layers performs focus control, andthe tracking beam applied to the servo layers performs only trackingcontrol. In other words, a focus of the tracking beam depends on thefocus control performed by the recording and reading beam. As a result,when the thickness tolerance becomes large, a focus position of thetracking beam varies to destabilize the tracking signal, which causes aproblem that sufficient tracking control cannot be performed. In orderto solve this problem, it is conceivable to introduce a focus servomechanism also into an optical system of the beam performing thetracking control. Correction of the thickness tolerance is, however,limited, and the introduction of the focus servo mechanism also causes aproblem of a large optical pickup.

In particular, if the recording and reading beam and the tracking beamshare one objective lens, the focus positions of the both beams need tobe shifted from each other by setting different spread angles for theboth beams being caused to enter the objective lens. As the differencebetween the spread angles of the both beams becomes larger, a shiftbetween the tracking control performed by the tracking beam and thetracking control required for the recording and reading beam becomeslarger. For example, there has been a problem that a tracking positionis greatly shifted from a recording position on a warped opticalrecording medium or the like.

Moreover, as the number of the recording and reading layers on theoptical recording medium is increased, a distance for moving a recordingand reading beam spot into a stacking direction increases. As a result,there has been a disadvantageous problem with comatic aberration causedby a tilt or the like in recording and reading.

Moreover, in the case of the techniques of Japanese Patent Laid-OpenNos. 2008-97693 and 2008-97694, as well as International Publication No.WO2008/099708, for example, there has been a problem that, when the beamdedicated to recording and reading passes through a desired recordingand reading layer, this leakage light is reflected by the servo layer tocause crosstalk. In particular, when the number of the recording andreading layers is increased, a reflectance of each recording and readinglayer must be reduced. Thus, there has been a problem of an increase inan amount of the leakage of the beam dedicated to recording and reading.

Furthermore, when the number of the recording and reading layers isincreased, the recording and reading layers are disposed over a widerange in a thickness direction in the optical recording medium. As aresult, a recording and reading optical pickup is required to focus thebeam on the wide range in the thickness direction. Thus, a largespherical aberration correction range must be set. Accordingly, therehas been a problem of a complicated and larger configuration of theoptical pickup, and also, a long seek time for the recording and readinglayers with the optical pickup.

Moreover, the increase in the number of the recording and reading layerscauses the capacity of the optical recording medium to increase, which,however, does not solely lead to improvement in a recording and readingspeed. For example, if the recording capacity of the optical recordingmedium increases without the improvement in the recording speed, therehas been a problem that a user has to wait longer in recording work andfeels reduction in convenience.

Furthermore, if information is recorded on an optical recording mediumincluding a plurality of recording and reading layers, OPC (OptimumPower Control) for optimizing recording laser power and its outputparameter needs to be performed for each recording and reading layer. Itshould be noted that, according to this OPC, a recording power level(Pw), an erasing power level (Pe) and the like of a laser are optimizedby recording random data in a trial writing area of each recording andreading layer while varying output power in a stepwise manner, and thenreproducing and analyzing this recorded data. With employment of theOPC, the laser power can be optimized immediately before recording, inconsideration of a usage environment such as a temperature, anindividual difference in a laser included in a drive, degradation ofeach recording and reading layer over time, and the like. However, therehas been a problem of an increase in a preparation time beforerecording, for this optimization.

In particular, when information is continuously recorded across theplurality of recording and reading layers, also in order to maintaincontinuity of an information transfer rate, a preparatory operation isrequired for previously performing the OPC for all the plurality ofrecording and reading layers that are recording targets, and retainingdifferent output parameters for the respective recording and readinglayers, in a storage memory. As a result, there has been a problem of afurther increase in the preparation time before recording.

Moreover, in the OPC, since the random data is recorded while the outputpower is varied in a stepwise manner, an extraordinarily high power beamis applied to the trial writing area to form an abnormal mark. Forexample, while the OPC is performed for a trial writing area of oneparticular recording and reading layer, if an abnormal mark has beenformed in a trial writing area of a recording and reading layer adjacentto this layer, noticeable reflection noise is caused by this abnormalmark so that correct OPC cannot be performed. In order to eliminate thisproblem, a larger trial writing area must be prepared so that the randomdata to be recorded in the OPC is controlled so as not to overlapbetween the adjacent recording and reading layers. As a result, therehas been a problem that, as the number of the recording and readinglayers is increased for the purpose of increasing the capacity of theoptical recording medium, the trial writing area of each recording andreading layer must be larger and a user data area is decreased.

As in Japanese Patent Laid-Open Nos. 2008-97693 and 2008-97694, as wellas International Publication No. WO2008/099708, in the optical recordingmedium provided with the servo layers and the recording and readinglayers separately, a shift in a radial direction can easily occur at arecording mark forming position on the recording and reading layerfarther from the servo layer. Accordingly, there has been a problem thatthe larger trial writing area also needs to be secured in anticipationof this shift, and the user data area is further decreased. Moreover,for example, in order to increase the recording and reading layers, whena plurality of servo layers are formed on one plane side of the opticalrecording medium, internal stress caused in film formation can easilyincline toward one side of the optical recording medium, and thuswarpage or distortion occurs on the optical recording medium. Since theshift in the radial direction can more easily occur at the recordingmark forming position, also due to this warpage or distortion, there hasbeen a problem that a further larger trial writing area must be secured.

According to the techniques of Japanese Patent Laid-Open Nos. 2008-97693and 2008-97694, there is a process of alternately stacking the recordingand reading layers and spacer layers, in production of the opticalrecording medium. Thus, the internal stress caused in each filmformation inclines toward one plane of the optical recording medium. Asa result, there has been a problem that large warpage or distortion caneasily occur on the optical recording medium. In particular, theincrease in the number of the recording and reading layers causes anamount of accumulated internal stress to increase, and also causes anamount of deformation of the optical recording medium to increase. Therehas been a problem that the deformation of the optical recording mediumcauses a tracking beam spot to be shifted from the recording and readingbeam spot, and causes a tracking property to be significantly degraded.

As seen from the above, as in the techniques of Japanese PatentLaid-Open Nos. 2008-97693 and 2008-97694, the optical recording mediumprovided with the servo layers and the recording and reading layersseparately is required to further reduce the warpage or the deformationamount of the medium. In order to reduce the warpage or the deformationamount, it is also conceivable to use an ultra-rigid body such as aglass substrate, which, however, increases the production costs.

Furthermore, if the plurality of servo layers are formed in one opticalrecording medium, positions of the grooves/lands of the respective servolayers may be shifted from one another. In this case, a relativeposition of a recording mark to be formed on the recording and readinglayer differs depending on which servo layer has been used forrecording. In such a situation, for example, complicated control isrequired to simultaneously record information on two recording andreading layers, or to simultaneously reproduce data recorded on the tworecording and reading layers.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above describedproblems, and it is an object of the present invention to provide anapproach for always stably performing tracking control for an opticalrecording medium including servo layers and recording and readinglayers. Moreover, it is another object of the present invention toimprove signal quality in recording and reading. It is another object ofthe present invention to provide an optical recording and readingapproach capable of improving a transfer rate even if multiple recordingand reading layers are provided in the optical recording medium. It isanother object of the present invention to suppress warpage ordeformation on a produced optical recording medium, and to enableefficient recording and reading. It is another object of the presentinvention to provide an optical recording and reading approach capableof suppressing complication of an optical pickup in an optical recordingand reading apparatus, while increasing the number of the recording andreading layers, and capable of efficiently performing recording andreading, and the like.

The present inventors have made extensive studies, and the above objectis achieved by the following means.

The present invention for achieving the above object is an opticalrecording and reading method for recording information in a recordingand reading layer in an optical recording medium, the optical recordingmedium comprising the recording and reading layer and a servo layer, therecording and reading layer being previously stacked or formed afterwardand having no concavo-convex pattern for tracking control, the servolayer having a concavo-convex pattern or a groove for tracking controlformed therein, wherein information is recorded in the recording andreading layer while tracking is performed using the servo layer.

In the optical recording and reading method for achieving the aboveobject according to the above invention, the optical recording mediumhas a plurality of the recording and reading layers, the methodcomprising: a servo layer using step of recording information in one ofthe recording and reading layers while performing tracking using theservo layer; and a recorded area using step of recording information inanother one of the recording and reading layers while performingtracking using information recorded area in the one of the recording andreading layers.

In the optical recording and reading method for achieving the aboveobject according to the above invention, a recording and reading beamhaving a second wavelength shorter than a first wavelength is applied tothe recording and reading layer to record or read information while atracking beam having the first wavelength is applied to the servo layerto perform tracking control, and wherein a reflectance of the servolayer at a time when light of the recording and reading beam having thesecond wavelength is applied through the recording and reading layer tothe servo layer is lower than a reflectance of the servo layer at a timewhen light of the tracking beam having the first wavelength is appliedthrough the recording and reading layer to the servo layer.

In the optical recording and reading method for achieving the aboveobject according to the above invention, the optical recording mediumhas a first set of a plurality of the recording and reading layersarranged on a side of a first surface, and a second set of a pluralityof the recording and reading layers arranged on a side of a secondsurface opposite to the first surface, wherein the number of layers ofthe second set of the recording and reading layers is equal to thenumber of layers of the first set of the recording and reading layers,and wherein a first recording and reading operation for recording orreading information by applying a first recording and reading beamthrough the first surface to the first set of the recording and readinglayers and a second recording and reading operation for recording orreading information by applying a second recording and reading beamthrough the second surface to the second set of the recording andreading layers are performed simultaneously.

In the optical recording and reading method for achieving the aboveobject according to the above invention, the optical recording mediumhas a substrate, the servo layer is formed on one face of the substrate,a first recording and reading layer is arranged on a side of the servolayer of the substrate, and a second recording and reading layer isarranged on a side opposite to the servo layer of the substrate, andinformation is recorded in the first recording and reading layer and thesecond recording and reading layer while tracking control is performedusing the servo layer.

In the optical recording and reading method for achieving the aboveobject according to the above invention, the optical recording andreading method further comprising: a first recording operation forrecording information by applying a first recording and reading beam toa first recording and reading layer while performing tracking control byapplying a tracking beam to the servo layer; and a second recordingoperation for recording information by applying a second recording andreading beam to a second recording and reading layer while performingtracking control using the tracking beam and the servo layer that arecommon with the first recording operation.

In the optical recording and reading method for achieving the aboveobject according to the above invention, a first recording and readinglayer is arranged on a side of a first surface of the optical recordingmedium with respect to the servo layer, and a second recording andreading layer is arranged on a side of a second surface of the opticalrecording medium with respect to the servo layer, the method comprising:a first recording operation for recording information in a firstrotation direction as viewed from the first surface by applying a firstrecording and reading beam through the first surface to the firstrecording and reading layer while performing tracking control byapplying a tracking beam to the servo layer; and a second recordingoperation for recording operation in a second rotation directionopposite to the first rotation direction as viewed from the secondsurface by applying a second recording and reading beam through thesecond surface to the second recording and reading layer whileperforming tracking control using the servo layer that is common withthe first recording operation, wherein the second recording operation isperformed simultaneously with the first recording operation.

The present invention for achieving the above object is an opticalrecording and reading apparatus that records information in a recordingand reading layer in an optical recording medium, the optical recordingmedium comprising the recording and reading layer and a servo layer, therecording and reading layer being previously stacked or formed afterwardand having no concavo-convex pattern for tracking control, the servolayer having a concavo-convex pattern or a groove for tracking controlformed therein, wherein the optical recording and reading apparatusrecords information in the recording and reading layer while performingtracking using the servo layer.

In the optical recording and reading apparatus for achieving the aboveobject according to the above invention, the optical recording mediumhas a first set of a plurality of the recording and reading layers on aside of a first surface, and a second set of a plurality of therecording and reading layers on a side of a second surface opposite tothe first surface, wherein the number of layers of the second set of therecording and reading layers is equal to the number of layers of thefirst set of the recording and reading layers, the optical recording andreading apparatus comprising: a first recording and reading opticalsystem that is arranged on the side of the first surface of the opticalrecording medium, and that records or reads information by applying afirst recording and reading beam through the first surface to the firstset of the recording and reading layers; and a second recording andreading optical system that is arranged on the side of the secondsurface of the optical recording medium, and that records or readsinformation by applying a second recording and reading beam through thesecond surface to the second set of the recording and reading layers.

In the optical recording and reading apparatus for achieving the aboveobject according to the above invention, the optical recording mediumhas a substrate, and a plurality of the recording and reading layers arearranged on a side of the servo layer with respect to the substrate, therecording and reading apparatus further comprising: a tracking opticalsystem that applies a tracking beam to the servo layer; a firstrecording and reading optical system that records information byapplying a first recording and reading beam to a first recording andreading layer while tracking control using the tracking optical systemis performed; and a second recording and reading optical system thatrecords information by applying a second recording and reading beam to asecond recording and reading layer while tracking control using thetracking optical system is performed.

In the optical recording and reading apparatus for achieving the aboveobject according to the above invention, the optical recording mediumhas a first set of a plurality of the recording and reading layersbetween a first surface of the optical recording medium and the servolayer, and a second set of a plurality of the recording and readinglayers between a second surface of the optical recording medium and theservo layer, the optical recording and reading apparatus furthercomprising: a tracking optical system that applies a tracking beam tothe servo layer; a first recording and reading optical system thatrecords information in a first rotation direction as viewed from thefirst surface by applying a first recording and reading beam through thefirst surface to the first recording and reading layer while trackingcontrol using the tracking optical system is performed; and a secondrecording and reading optical system that records information in asecond rotation direction opposite to the first rotation direction asviewed from the second surface by applying a second recording andreading beam through the second surface to the second recording andreading layer while tracking control using the tracking optical systemis performed, wherein the second recording and reading optical systemperforms the recording simultaneously with the recording which the firstrecording and reading optical system performs.

The present invention for achieving the above object is an opticalrecording medium comprising a servo layer having a concavo-convexpattern or a groove for tracking control and a recording and readinglayer having no concavo-convex pattern for tracking control, therecording and reading layer being previously stacked or formedafterward, wherein information is recorded or read by applying arecording and reading beam to the recording and reading layer whileapplying a tracking beam to the servo layer to perform tracking control.

In the optical recording medium for achieving the above object accordingto the above invention, information is recorded or read by applying arecording and reading beam having a second wavelength shorter than afirst wavelength to the recording and reading layer while applying atracking beam having the first wavelength to the servo layer to performtracking control, and wherein a reflectance of the servo layer at a timewhen light of the recording and reading beam having the secondwavelength is applied through the recording and reading layer to theservo layer is lower than a reflectance of the servo layer at a timewhen light of the tracking beam having the first wavelength is appliedthrough the recording and reading layer to the servo layer.

In the optical recording medium for achieving the above object accordingto the above invention, the optical recording medium further comprisinga substrate, wherein the servo layer is formed on one face of thesubstrate, wherein a first recording and reading layer is arranged on aside of the servo layer of the substrate, and a second recording andreading layer is arranged on a side opposite to the servo layer of thesubstrate, and wherein information is recorded in the first recordingand reading layer and the second recording and reading layer whiletracking control is performed using the servo layer.

In the optical recording medium for achieving the above object accordingto the above invention, the optical recording medium further comprising,as the servo layer: a first servo layer having a concavo-convex patternor a groove for the tracking control in a first spiral direction; and asecond servo layer having a concavo-convex pattern or a groove for thetracking control in a second spiral direction opposite to the firstspiral direction, wherein a first set of a plurality of the recordingand reading layers are arranged on a side of a first surface of theoptical recording medium with respect to the first and second servolayers, and wherein a second set of a plurality of the recording andreading layers are arranged on a side of a second surface of the opticalrecording medium with respect to the first and second servo layers.

The present invention for achieving the above object is a method ofmanufacturing an optical recording medium, the method comprising thesteps of: forming a servo layer having a concavo-convex pattern or agroove for tracking control on one face of a substrate made of a lighttransmitting material; simultaneously stacking a first buffer layer tobe arranged on a side of the servo layer of the substrate and a secondbuffer layer to be arranged on a side opposite to the servo layer of thesubstrate; and simultaneously stacking a first recording and readinglayer to be arranged on a side of the first buffer layer and a secondrecording and reading layer to be arranged on a side of the secondbuffer layer, wherein the first recording and reading layer has a planerstructure with no concavo-convex pattern for tracking control, and thesecond recording and reading layer has a planer structure with noconcavo-convex pattern for tracking control.

According to the present invention, for the optical recording mediumincluding the servo layers and the recording and reading layers, it ispossible to record information on the recording and reading layers whilealways stably performing the tracking control for the optical recordingmedium.

According to the present invention, in the optical recording mediumincluding the servo layers and the recording and reading layers, it ispossible to improve the signal quality in recording and reading.

Moreover, it is possible to improve the transfer rate even if themultiple recording and reading layers are provided in the opticalrecording medium.

Furthermore, for the optical recording medium including the servo layersand the recording and reading layers, it is possible to efficientlyperform recording and reading, while suppressing the warpage or thedeformation.

It is possible to suppress the complication of the optical pickup in theoptical recording and reading apparatus, while increasing the number ofthe recording and reading layers, and to efficiently perform recordingand reading.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a structure of an optical pickupthat realizes an optical recording and reading method of an opticalrecording medium according to an embodiment of the present invention;

FIG. 2 is a sectional view illustrating a multilayer structure of theoptical recording medium;

FIG. 3 is an enlarged sectional view illustrating a recording procedureof the optical recording and reading method;

FIG. 4 is an enlarged sectional view illustrating a recording procedureof the optical recording and reading method;

FIG. 5 is a sectional view illustrating another example of themultilayer structure of an optical recording medium used in an opticalrecording and reading method according to an embodiment of the presentinvention;

FIG. 6 is an enlarged sectional view illustrating another example of therecording procedure of the optical recording and reading method;

FIG. 7 is an enlarged sectional view illustrating another example of therecording procedure of the optical recording and reading method;

FIG. 8 is a block diagram illustrating an optical recording medium andan internal configuration of an optical pickup which realizes opticalrecording and reading according to a second embodiment of the presentinvention;

FIG. 9 is a sectional view illustrating a multilayer structure of theoptical recording medium;

FIG. 10A is an enlarged sectional view illustrating a recordingprocedure of an optical recording and reading method with respect to theoptical recording medium, and FIG. 10B is an enlarged sectional viewillustrating a reproducing procedure;

FIG. 11A is a sectional view illustrating a multilayer structure of anoptical recording medium according to a third embodiment, and FIG. 11Bis an enlarged sectional view illustrating a recording and readingprocedure with respect to the optical recording medium;

FIG. 12A is a sectional view illustrating another example of themultilayer structure of the optical recording medium according to thethird embodiment, and FIG. 12B is an enlarged sectional viewillustrating the recording and reading procedure with respect to theoptical recording medium;

FIG. 13 is a sectional view illustrating a multilayer structure of anoptical recording medium according to a fourth embodiment;

FIG. 14 is a diagram illustrating an overall configuration of an opticalpickup that provides optical recording and reading according to thefourth embodiment;

FIG. 15 is a sectional view illustrating a partially enlarged view ofthe multilayer structure of an optical recording medium according to apractical example;

FIG. 16 is a table showing evaluation results of practical examples andcomparative examples;

FIG. 17 is a photographic view showing output waveforms of readingsignals in a practical example and a comparative example;

FIG. 18 is a sectional view illustrating another configuration exampleof the optical recording medium according to the second embodiment ofthe present invention;

FIG. 19 is a block diagram illustrating an overall configuration of anoptical recording and reading apparatus and an optical recording mediumfor realizing an optical recording and reading method according to afifth embodiment of the present invention;

FIG. 20 is a block diagram illustrating an internal configurationexample of a first optical pickup of the optical recording and readingapparatus;

FIG. 21 is a block diagram illustrating an internal configurationexample of a second optical pickup of the optical recording and readingapparatus;

FIG. 22 is a sectional view illustrating a multilayer structure of theoptical recording medium;

FIG. 23A is a sectional view illustrating a procedure for producing theoptical recording medium;

FIG. 23B is a sectional view illustrating the procedure for producingthe optical recording medium;

FIG. 23C is a sectional view illustrating the procedure for producingthe optical recording medium;

FIG. 23D is a sectional view illustrating the procedure for producingthe optical recording medium;

FIG. 24 is a flowchart illustrating a procedure for setting recordingpower by the optical recording and reading apparatus;

FIGS. 25A to 25D are enlarged sectional views illustrating a procedurefor execution of OPC on the optical recording medium according to theoptical recording and reading method;

FIG. 26 is a graph illustrating changes in recording power when OPC isperformed by the optical recording and reading apparatus;

FIGS. 27A to 27D are enlarged sectional views illustrating a procedurefor recording on the optical recording medium according to the opticalrecording and reading method;

FIG. 28 is an enlarged sectional view illustrating a procedure forreproducing from the optical recording medium according to the opticalrecording and reading method;

FIG. 29 is a sectional view illustrating another example of themultilayer structure of the optical recording medium to which theoptical recording and reading method is applied;

FIG. 30 is a sectional view illustrating still another example of themultilayer structure of the optical recording medium to which theoptical recording and reading method is applied;

FIG. 31 is a sectional view illustrating a further example of themultilayer structure of the optical recording medium to which theoptical recording and reading method is applied;

FIG. 32 is a flowchart illustrating a procedure for setting of recordingpowers by an optical recording and reading apparatus according to asixth embodiment of the present invention;

FIG. 33 is an enlarged sectional view illustrating a procedure ofexecution of OPC with respect to an optical recording medium accordingto an optical recording and reading method of the sixth embodiment ofthe present invention;

FIG. 34 is an enlarged sectional view illustrating a procedure forrecording in the optical recording medium according to the opticalrecording and reading method;

FIG. 35 is an enlarged sectional view illustrating a procedure forrecording in the optical recording medium according to the opticalrecording and reading method;

FIG. 36 is an enlarged sectional view illustrating a procedure ofreproduction from the optical recording medium according to the opticalrecording and reading method;

FIG. 37 is an enlarged sectional view illustrating a procedure ofrecording on an optical recording medium according to an opticalrecording and reading method of a seventh embodiment of the presentinvention;

FIG. 38 is an enlarged sectional view illustrating the procedure ofrecording on the optical recording medium according to the opticalrecording and reading method;

FIG. 39 is an enlarged sectional view illustrating a procedure ofreproducing from the optical recording medium according to the opticalrecording and reading method;

FIG. 40 is a sectional view illustrating another example of a multilayerstructure of the optical recording medium to which the optical recordingand reading method is applied;

FIG. 41 is a sectional view illustrating another example of a recordingprocedure of the optical recording and reading method and anotherexample of the optical recording medium;

FIG. 42 is an enlarged sectional view illustrating another example of arecording procedure on an optical recording medium according to theoptical recording and reading method;

FIG. 43 is a block diagram illustrating an overall configuration of anoptical pickup that provides optical recording and reading on an opticalrecording medium according to an eighth embodiment of the presentinvention;

FIG. 44 is a block diagram illustrating an internal configurationexample of the optical pickup;

FIG. 45 is a block diagram illustrating another internal configurationexample of the optical pickup;

FIG. 46 is a sectional view illustrating a multilayer structure of theoptical recording medium;

FIG. 47A is an enlarged sectional view illustrating a recordingprocedure on the optical recording medium by an optical recording andreading method;

FIG. 47B is an enlarged sectional view illustrating the recordingprocedure on the optical recording medium by the optical recording andreading method;

FIG. 47C is an enlarged sectional view illustrating the recordingprocedure on the optical recording medium by the optical recording andreading method;

FIG. 47D is an enlarged sectional view illustrating the recordingprocedure on the optical recording medium by the optical recording andreading method;

FIG. 48 is a sectional view illustrating another example of themultilayer structure of the optical recording medium according to thepresent embodiment;

FIG. 49 is a sectional view illustrating yet another example of themultilayer structure of the optical recording medium according to thepresent embodiment;

FIG. 50 is a sectional view illustrating still another example of themultilayer structure of the optical recording medium according to thepresent embodiment;

FIG. 51 is a block diagram illustrating an overall configuration of anoptical recording and reading apparatus and an optical recording mediumfor achieving an optical recording and reading method according to aninth embodiment of the present invention;

FIG. 52 is a block diagram illustrating an internal configurationexample of a first optical pickup in the optical recording and readingapparatus;

FIG. 53 is a block diagram illustrating an internal configurationexample of a second optical pickup in the optical recording and readingapparatus;

FIG. 54 is a sectional view illustrating a multilayer structure of theoptical recording medium;

FIG. 55A is a sectional view illustrating a procedure for producing theoptical recording medium;

FIG. 55B is a sectional view illustrating a procedure for producing theoptical recording medium;

FIG. 55C is a sectional view illustrating a procedure for producing theoptical recording medium;

FIG. 55D is a sectional view illustrating a procedure for producing theoptical recording medium;

FIG. 55E is sectional view illustrating a procedure for producing theoptical recording medium;

FIG. 56 is an enlarged sectional view illustrating a recording procedurefor an optical recording medium according to the optical recording andreading method;

FIG. 57 is an enlarged sectional view illustrating a recording procedurefor an optical recording medium according to the optical recording andreading method;

FIG. 58 is an enlarged sectional view illustrating a reproducingprocedure for an optical recording medium according to the opticalrecording and reading method;

FIG. 59 is a perspective diagram illustrating a recording and readingprocedure for an optical recording medium according to the opticalrecording and reading method;

FIG. 60 is an enlarged sectional view illustrating another reproducingprocedure for an optical recording medium according to the opticalrecording and reading method;

FIG. 61 is a sectional view illustrating another example multilayerstructure of an optical recording medium to which the optical recordingand reading method is applied;

FIG. 62 is a sectional view illustrating another example multilayerstructure of an optical recording medium to which the optical recordingand reading method is applied;

FIG. 63 is a sectional view illustrating another example multilayerstructure of an optical recording medium to which the optical recordingand reading method is applied; and

FIG. 64 is a sectional view illustrating another example multilayerstructure of an optical recording medium to which the optical recordingand reading method is applied.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be explained below in detailwith reference to the accompanying drawings.

FIG. 1 shows an optical recording medium 10 according to a firstembodiment of the present invention and a configuration of an opticalpickup 90 used for recording and reading in this optical recordingmedium 10. The optical pickup 90 includes a first optical system 100 anda second optical system 200. The first optical system 100 denotes anoptical system (i.e. recording and reading optical system) that performsrecording/reading for a group of recording and reading layers 14 of theoptical recording medium 10. The second optical system 200 denotes anoptical system (i.e. tracking optical system) that performs trackingcontrol using a servo layer 18 (described later) and a recorded area ofthe group of recording and reading layers 14 when recording informationin the group of recording and reading layers 14 using the first opticalsystem 100.

A divergent recording and reading beam 170 with a blue wavelength of 380to 450 nm (405 nm in this case), which is emitted from a light source101 of the first optical system 100, transmits through a collimated lens153 having spherical aberration correcting means 193 and enters into apolarizing beam splitter 152. The beam 170 having entered into thepolarizing beam splitter 152 transmits through the polarizing beamsplitter 152, converts into a circularly polarized light by furthertransmission in a quarter-wave plate 154 and then enters into a beamsplitter 260 of the second optical system 200. This beam splitter 260 isset to have a high transmittance and low reflectance. To be morespecific, it is set such that the ratio of the transmittance to thereflectance is 10 times or more. Therefore, the beam 170 transmitsthrough the beam splitter 260 and converts into a converging beam by anobjective lens 156. This beam 170 converges into one of the group ofrecording and reading layers 14 and the servo layer 18 of recording andreading targets which are formed inside the optical recording medium 10.

The objective lens 156 is controlled by an aperture 155, where thenumerical aperture NA is set between 0.70 and 0.90 (0.85 in this case).For example, the beam 170 reflected in the group of recording andreading layers 14 transmits through the objective lens 156, the beamsplitter 260 and the quarter-wave plate 154, converts into a linearpolarized light different from that on an outward path by 90 degrees andthen is reflected in the polarizing beam splitter 152.

The beam 170 reflected in the polarizing beam splitter 152 goes througha condenser lens 159, converts into a converging light and enters intoan optical detector 132 via a cylindrical lens 157. Here, an astigmatismis attached to the beam 170 when the beam 170 goes through thecylindrical lens 157.

The optical detector 132 has four light receiving unit (not shown) andoutputs current signals corresponding to respective amounts of receivedlight. From these current signals, for example, a focus error(hereinafter referred to as “FE”) signal by an astigmatic method, atracking error (hereinafter referred to as “TE”) signal by a push-pullmethod limited on reproduction and a reading signal of informationrecorded in the optical recording medium 10 are generated. The FE signaland the TE signal are subjected to amplification and phase compensationto a desired level, and then feedback-supplied to actuators 191 and 192and subjected to focus control and tracking control. It should be notedthat tracking control in the first optical system 100 is utilized onlyat the time of reproduction.

A divergent tracking control beam 270 with a blue wavelength of 380 to450 nm (405 nm in this case), which is emitted from a light source 201of the second optical system 200, transmits through a collimated lens253 having spherical aberration correcting means 293 and enters into apolarizing beam splitter 252. The beam 270 having entered into thepolarizing beam splitter 252 transmits through the polarizing beamsplitter 252, further transmits through a quarter-wave plate 254 for thesecond optical system, converts into a circularly polarized light andthen is reflected in the beam splitter 260. This beam 270 furtherconverts into a converging beam in the objective lens 156 and convergesinto one of the servo layer 18 and the group of recording and readinglayers 14 which are formed inside the optical recording medium 10. Forexample, the beam 270 reflected in the servo layer 18 transmits throughthe objective lens 156 and is reflected in the beam splitter 260,converts at the quarter-wave plate 254 into a linear polarized lightdifferent from that on an outward path by 90 degrees and then is furtherreflected in the polarizing beam splitter 252. The beam 270 reflected inthe polarizing beam splitter 252 goes through a condenser lens 259,converts into a converging light and enters into an optical detector 232via a cylindrical lens 257. Here, an astigmatism is attached to the beam270 when the beam 270 goes through the cylindrical lens 257.

The optical detector 232 has four light receiving unit (not shown) andoutputs current signals corresponding to respective amounts of receivedlight. From these current signals, a TE signal by a push-pull method isgenerated. It should be noted that, in a case where information isrecorded even in the servo layer 18, a reading signal may be generatedfrom the current signals. On the side of this optical detector 232,although an FE signal has not to be generated, it is natural that an FEsignal may be generated.

It should be noted that, as described above, the beam splitter 260 isset to have a high transmittance and low reflectance. Accordingly, apart of a return light, which is emitted from the light source 101 ofthe first optical system 100 and reflected in part of the group ofrecording and reading layers 14, is reflected in the beam splitter 260and proceeds to the side of the second optical system 200. By contrast,a large part of a return light, which is emitted from the light source201 of the second optical system 200 and reflected in the servo layer 18or the recorded area in the group of recording and reading layers 14,transmits through the beam splitter 260 and proceeds to the side of thefirst optical system 100. That is, in the first optical system 100 andthe second optical system 200, as long as the substantially same lightsource with a blue wavelength of 380 to 450 nm is adopted, it isinevitable that their return lights are mixed. However, since the firstoptical system 100 and the second optical system 200 have differentfocus positions in the optical recording medium 10 and therefore spreadangles of the beams 170 and 270 are different from each other, byextracting one of the beams 170 and 270 using a given-shape slit oraperture (not shown) and then entering it into the optical detector 132or 232, an influence due to mixing is eliminated.

Especially, if it is set that a difference between a focus position ofthe beam 170 in the first optical system 100 in the optical recordingmedium 10 and a focus position of the beam 270 in the second opticalsystem 200 in the optical recording medium 10 always falls within acertain range, it is possible to simplify the structures of theabove-noted slit and aperture, so that it is possible to separate thebeams more easily. To stabilize the focus distance gap, it is preferablethat the focus position of the recording and reading beam 170 and thefocus position of the beam 270 for servo are closer to each otherbecause the error becomes smaller.

When information is recorded in the group of recording and readinglayers 14 in the first optical system 100, a TE signal of the secondoptical system 200 is subjected to amplification and phase compensationto a desired level, and then feedback-supplied to the actuators 191 and192 and subjected to tracking control. As a result, based on thetracking control in the second optical system 200, the first opticalsystem 100 is made to record information in the group of recording andreading layers 14. It should be noted that, in the present embodiment,when information recorded in the group of recording and reading layers14 is reproduced, the first optical system 100 is made to uniquelyperform tracking control utilizing a recording mark on the group ofrecording and reading layers 14. On the other hand, it is naturallypossible to perform reproduction utilizing the tracking control in thesecond optical system 200.

FIG. 2 shows a cross-section structure of the optical recording medium10 according to the present embodiment in a large size.

The optical recording medium 10 has a discoid shape having an externaldiameter of approximately 120 mm and a thickness of approximately 1.2mm. This optical recording medium 10 is configured with a cover layer11, the group of recording and reading layers 14, a group ofintermediate layers 16, a buffer layer 17, the servo layer 18 and asupport substrate 12 from the side of a light incident surface 10A.

The group of recording and reading layers 14 is configured with first tosixth recording and reading layers 14A to 14F, which are configured tobe able to record information. These first to sixth recording andreading layers 14A to 14F employ a planar structure having noconcavo-convex pattern or grooves for tracking control, and, when therecording beam 170 of high energy is applied from the first opticalsystem 100, form recording marks. It should be noted that, as a kind ofthis group of recording and reading layers 14, there are a write-oncerecording and reading layer in which information can be added but cannotbe rewritten, and a rewritable recording and reading layer in whichinformation can be rewritten.

The support substrate 12 denotes a discoid-shaped substrate having athickness of 1.0 mm and a diameter of 120 mm for maintaining a thickness(of approximately 1.2 mm) required for the optical recording medium, andthe servo layer 18 is formed on a surface of the side of the lightincident surface 10A of this support substrate 12. To be more specific,a land 18A and a groove 18B are formed in a spiral manner in a directionfrom around the center part to the outer edge in the side of the lightincident surface 10A of the support substrate 12. These land 18A andgroove 18B function as a concavo-convex pattern (or grooves) fortracking control and guide the beam 270 of the second optical system200.

It should be noted that it is possible to use various materials as amaterial of the support substrate 12, such as a glass, ceramics andresin. Out of these, a resin is preferable in view of moldability. Resinexamples include a polycarbonate resin, olefin resin, acrylic resin,epoxy resin, polystyrene resin, polyethylene resin, polypropylene resin,silicone resin, fluorine resin, ABS resin and urethane resin. Out ofthese, the polycarbonate resin and the olefin resin are especiallypreferable in view of workability. It should be noted that the supportsubstrate 12 does not operate as a light path of the beam 270 andtherefore needs not have a high optical transparency.

The servo layer 18 formed on the support substrate 12 is configured byforming tracking control a concavo-convex pattern (i.e. groove and land)and a reflecting layer on the surface of the support substrate 12.Especially, in the present embodiment, a recording film that can recordinformation is provided. This recording film has substantially the samefilm structure as those of the recording and reading layers 14A to 14F(described later). It should be noted that, if an information recordingfunction is not necessary in this servo layer 18, a metal layer such asAg may be formed to simply function as an optical reflecting film.

A pitch P1 of adjacent lands 18A or grooves 18B in the servo layer 18 isset to be equal to or lower than 0.37 μm (e.g. within a range between0.26 μm and 0.35 μm). To be more specific, the pitch P1 is set to avalue close to 0.32 μm. A track pitch P2 of the recording marks recordedin the recording and reading layers 14A to 14F is set in substantiallythe same way as the pitch P1 of the lands 18A and the grooves 18B. As aresult, the track pitch P2 between recording marks is set to be lowerthan 0.37 μm. Preferably, it is set within a range between 0.26 μm and0.35 μm. More preferably, it is set to a value close to 0.32 μm.

As a result, the track pitch P2 recorded in the recording and readinglayers 14A to 14F has a value around 0.32 μm compatible to the BDstandard. The pitch P1 (around 0.32 μm) of the lands 18A or the grooves18B in the servo layer 18 has a size in which tracking by the beam 270of a blue wavelength range is sufficiently possible.

The buffer layer 17 is configured with a light-transmitting acrylicultraviolet curable resin and corresponds to the film thickness of oneof first to fifth intermediate layers 16A to 16E (described later).Here, it is set to 12 μm which is one of the film thicknesses of thefirst to fifth intermediate layers 16A to 16E.

The first to sixth recording and reading layers 14A to 14F, which arestacked on the side of the light incident surface 10A of the bufferlayer 17, each have a three-layer structure in which a dielectric filmis stacked on both sides of a write-once recording film (not shown). Itshould be noted that the first to sixth recording and reading layers 14Ato 14F are configured such that, for example, the optical reflectance,absorptance and transmittance are optimized for the beam 170 of a bluewavelength range (i.e. short wavelength) in the first optical system100.

The dielectric film of each recording and reading layer also has a basicfunction of protecting a write-once recording film and plays a role ofenlarging an optical characteristic gap between before and afterrecording mark formation.

It should be noted that, in a case where the beam 170 is applied, therecord sensitivity is likely to decrease when energy absorbed in thedielectric films is higher. Therefore, to prevent this, it is preferableto select a material having a low absorption coefficient (k) in awavelength range of 380 nm to 450 nm (particularly 405 nm), as amaterial of those dielectric films. It should be noted that TiO2 is usedas a material of the dielectric films in the present embodiment.

A write-once recording film between dielectric films denotes a film inwhich an irreversible recording mark is formed, and there is a large gapof reflectance with respect to the beam 170 between a part in which therecording mark is formed and other parts (i.e. blank range). As aresult, it is possible to record/read data.

The write-once recording film is formed to contain materials includingBi and O as major ingredients. This write-once recording film functionsas an inorganic reaction film and is configured such that thereflectance significantly varies depending on a chemical or physicalchange by heat of laser light. As specific materials, it is preferableto contain Bi—O or Bi-M-O (where M is at least one kind of elementselected from Mg, Ca, Y, Dy, Ce, Tb, Ti, Zr, V, Nb, Ta, Mo, W, Mn, Fe,Zn, Al, In, Si, Ge, Sn, Sb, Li, Na, K, Sr, Ba, Sc, La, Nd, Sm, Gd, Ho,Cr, Co, Ni, Cu, Ga and Pb) as major ingredients. It should be noted thatBi—Ge—O are used as materials of a write-once recording film in thepresent embodiment.

It should be noted that, although a case has been described where awrite-once recording film is adopted in the first to sixth recording andreading layers 14A to 14F, it is equally possible to adopt aphase-change recording film in which iterative recording is possible. Inthis case, it is preferable that the phase-change recording filmcontains SbTeGe as major ingredients.

The group of intermediate layers 16 has the first to fifth intermediatelayers 16A to 16E in order from the side farthest from the lightincident surface 10A, where these layers are stacked between the firstto sixth recording and reading layers 14A to 14F. The first to fifthintermediate layers 16A to 16E are each configured with an acrylic orepoxy ultraviolet curable resin. It is preferable to set the filmthicknesses of these first to fifth intermediate layers 16A to 16E tovalues equal to or less than 20 μm to increase the number of layers,where the film thickness of the first intermediate layer 16A is 16 μm,that of the second intermediate layer 16B is 12 μm, that of the thirdintermediate layer 16C is 16 μm, that of the fourth intermediate layer16D is 12 μm and that of the fifth intermediate layer 16E is 16 μm. Thatis, intermediate layers having two kinds of film thicknesses (16 μm and12 μm) are alternately stacked. As a result, as the inter-layerdistances between the first to sixth recording and reading layers 14A to14F, the first distance (16 μm) and the second distance different fromthis first distance (12 μm) are alternately set in order from the sideof the light incident surface. Here, the gap between the first distanceand the second distance is set to 4 μm. By this means, it is possible toreduce the inter-layer crosstalk. It is natural that the same filmthickness may be set for all of the group of intermediate layers 16.

The cover layer 11 is configured with a light-transmitting acrylicultraviolet curable resin in the same way as in the group ofintermediate layers 16, where the film thickness is set to 38 μm.

As a result of configuring the optical recording medium 10 as above, theservo layer 18 is in a position 0.122 mm (i.e. 122 μm) apart from thelight incident surface 10A, the first recording and reading layer 14Awhich is the farthest from the light incident surface 10A in the groupof recording and reading layers 14 is in a position 0.11 mm (i.e. 110μm) apart from the light incident surface 10A, the second recording andreading layer 14B is in a position 94 μm apart from the light incidentsurface 10A, the third recording and reading layer 14C is in a position82 μm apart from the light incident surface 10A, the fourth recordingand reading layer 14D is in a position 66 μm apart from the lightincident surface 10A, the fifth recording and reading layer 14E is in aposition 54 μm apart from the light incident surface 10A, and the sixthrecording and reading layer 14F which is the nearest to the lightincident surface 10A is in a position 38 μm apart from the lightincident surface 10A. Further, the entire thickness of the group ofrecording and reading layers 14 (i.e. the distance between the firstrecording and reading layer 14A and the sixth recording and readinglayer 14F) is 72 μm.

Also, in the optical recording medium 10 of the present embodiment,compared to the group of recording and reading layers 14, the servolayer 18 is placed in a position farther from the light incident surface10A. By this means, it is possible to reduce a harmful influence givenfrom the land 18A and the groove 18B for tracking to the recording andreading beam 170 applied to the group of recording and reading layers14.

Next, a method for producing the optical recording medium 10 accordingto the present embodiment will be explained.

First, by a polycarbonate resin mold injection method using a metalstamper, the support substrate 12 in which grooves and lands are formedis produced. Using the mold injection type, basic information to be heldin advance at the time of medium production is preformatted in thissupport substrate 12, where the basic information includes addressinformation of the group of recording and reading layers 14, recordingconditions including a recording and reading power, and position orinter-layer distance of the recording and reading layers 14A to 14F. Tobe more specific, basic information is preformed using wobble of theland 18A or the groove 18B. It should be noted that a method ofproducing the support substrate 12 is not limited to the injectionmolding method and a 2P method or other methods are possible.

After that, in the support substrate 12, the servo layer 18 is formed onthe surface of the side on which grooves and lands are provided. Theservo layer 18 is formed by stacking a dielectric film, write-oncerecording film and dielectric film in order (i.e. reflecting film andprotect film) using a sputtering method or vapor-phase epitaxial methodto function as a recording film.

Next, the buffer layer 17 is formed on the servo layer 18. The bufferlayer 17 is formed by, for example, filming viscosity-controlled acrylicor epoxy ultraviolet curable resins in a spin coat method andirradiating these with ultraviolet for curing. It should be noted that,instead of ultraviolet curable resins, it can also be formed byattaching a light transmitting sheet made of light transmitting resinsonto the servo layer 18 using an adhesive bond or adhesive compound.Also, if necessary, in the case of forming grooves or pits required forrecording in this buffer layer 17, it is possible to form the grooves orpits by attaching a light transmitting resin stamper to spin-coatedultraviolet curable resins in the 2P method and irradiating these withultraviolet for curing.

Next, the first recording and reading layer 14A is formed. To be morespecific, it is formed by layering a dielectric film, write-oncerecording film and dielectric film in order using a vapor-phaseepitaxial method. Especially, it is preferable to use a sputteringmethod. After that, the first intermediate layer 16A is formed on thefirst recording and reading layer 14A. The first intermediate layer 16Ais formed by, for example, filming viscosity-controlled ultravioletcurable resins in a spin coat method and irradiating these ultravioletcurable resins with ultraviolet for curing. By repeating this procedure,the second recording and reading layer 14B, the second intermediatelayer 16B, and so on, are stacked in order.

When the sixth recording and reading layer 14F has been layered, thecover layer 11 is formed on the result to complete the optical recordingmedium 10. It should be noted that the cover layer 11 is formed by, forexample, filming viscosity-controlled acrylic or epoxy ultravioletcurable resins in a spin coat method and irradiating these withultraviolet for curing. It should be noted that, although theabove-noted producing method has been described in the presentembodiment, the present invention is not limited to this producingmethod and other producing technologies are adoptable.

Next, with reference to FIG. 3, a method for recording and readinginformation in the optical recording medium 10 of the preset embodimentwill be explained using the optical pickup 90.

<Recording in Servo Layer/General-Purpose Step>

When information is recorded in the servo layer 18 of this opticalrecording medium 10, a conventional known method is used. To be morespecific, using only the first optical system 100, information isrecorded on the groove 18B while applying the beam 170 to the servolayer 18 and performing tracking control and focus control using thegroove 18B. The same applies to reproduction.

<Recording in First Recording and Reading Layer/Servo Layer Using Step>

When information is recorded in the first recording and reading layer14A adjacent to the servo layer 18, first, the beam 270 of the bluewavelength range of the second optical system 200 is applied to theservo layer 18 to perform tracking. To be more specific, as shown inFIGS. 3A and 3B, a spot of the beam 270 is applied to the groove 18B inthe servo layer 18 to perform tracking. At the same time of thisoperation, the recording beam 170 of the blue wavelength range of thefirst optical system 100 is applied to the first recording and readinglayer 14A.

As a result, while performing tracking of the groove 18B, information isrecorded in the first recording and reading layer 14A along the groove18B. As a result, the track pitch P2 of a recording mark formed in thefirst recording and reading layer 14A matches the pitch P1 between thegrooves 18B. It should be noted that, in the servo layer 18, forexample, information related to a basic system about the opticalrecording medium 10 and information related to the number of layers inthe group of information recording layers 14 are recorded in advance inrecording pits or BCA (Burst Cutting Area), so that these items ofinformation are reliably read before tracking control starts. The basicinformation related to the optical recording medium contains a positionof the servo layer 18, positions of the first to sixth recording andreading layers 14A to 14F and rules related to the inter-layer distancein the group of recording and reading layers.

When required information has been recorded in the first recording andreading layer 14A, additional information (such as address informationrelated to recording and content information) of this time is recordedin the side of the servo layer 18 and the operation ends. It should benoted that, although the recording in the servo layer 18 in this case isperformed using the beam 170 as the general-purpose step describedabove, it is natural that the recording may be directly performed usingthe beam 270 subjected to tracking control. By gathering managementinformation in the servo layer 18, it is possible to easily find fromwhich the recording starts at the next recording/reading.

It should be noted that, if the servo layer 18 does not have a recordinglayer, for example, it is preferable to maintain a management area inpart of the first recording and reading layer 14A which is the farthestfrom the light incident surface 10A (i.e. which is the closest to theservo layer 18), and record the management information therein.

After that, in a case where the recording of information with respect tothe first recording and reading layer 14A restarts, first, themanagement information recorded in the servo layer 18 is reproduced, aposition in which the previous recording is completed in the firstrecording and reading layer 14A is checked, and the recording continuesfrom the position. By this means, in the servo layer using step, arecording operation reliably continues until the recording ofinformation with respect to the entire data area in the first recordingand reading layer 14A is completed. Even in a case where an availabledata area is provided in a halfway manner or an unrecorded space has tobe maintained if necessary, information continuity is maintained byrecording dummy information therein. As a result, the entire data areain the first recording and reading layer 14A becomes a recorded area.

<Recording in Second Recording and Reading Layer/Recorded Area UsingStep>

When information has been recorded in the entire data area of the firstrecording and reading layer 14A, next, information is recorded in thesecond recording and reading layer 14B adjacent to the first recordingand reading layer 14A. In this case, as shown in FIGS. 4A and 4B, first,by applying the tracking control beam 270 of the second optical system200 to the recorded area of the first recording and reading layer 14A,tracking control is performed using the reading signals. Together withthis operation, recording is performed by applying the recording beam170 of the first optical system 100 to the second recording and readinglayer 14B. It should be noted that, after the recording of requiredinformation is completed, additional information (such as addressinformation related to recording and content information) of this timeis recorded in the side of the servo layer 18 and the operation ends.

After that, in a case where the recording of information with respect tothe second recording and reading layer 14B restarts, first, themanagement information recorded in the servo layer 18 is reproduced, aposition in which the previous recording is completed in the secondrecording and reading layer 14B is checked, and the recording continuesfrom the position. By this means, in the recorded area using step, arecording operation reliably continues until the recording ofinformation with respect to the entire data area in the second recordingand reading layer 14B is completed. Even in a case where an availabledata area is provided in a halfway manner or an unrecorded space has tobe maintained if necessary, information continuity is maintained byrecording dummy information. As a result, the entire data area in thesecond recording and reading layer 14B becomes a recorded area.

<Recording in Third and Later Recording and Reading Layers/Recorded AreaUsing Step>

When information has been recorded in the entire data area of the secondrecording and reading layer 14B, next, information is recorded in thethird recording and reading layer 14C adjacent to the second recordingand reading layer 14B. In this case, by applying the tracking controlbeam 270 of the second optical system 200 to the recorded area of thesecond recording and reading layer 14B, tracking control is performedusing the reading signals. Together with this operation, recording isperformed by applying the recording beam 170 of the first optical system100 to the third recording and reading layer 14C. The followingprocedure is the same as in the recorded area using step explained inthe second recording and reading layer 14B, and therefore an explanationwill be omitted. By repeating the above-noted procedure, information isrecorded in the first to sixth recording and reading layers 14A to 14Fin order.

It should be noted that, for example, when information recorded in thefirst recording and reading layer 14A is reproduced, first, the servolayer 18 is reproduced using the beam 170 of the first optical system100 to read the above-noted basic system and additional informationbased on the record (such as content information recorded in the firstrecording and reading layer 14A). After that, based on these items ofinformation, the beam 170 of the first optical system 100 is moved tothe first recording and reading layer 14A to access a predeterminedaddress and perform reproduction. At this time, tracking may beperformed using a recording mark recorded in the first recording andreading layer 14A. Therefore, it is possible to eliminate the beam 270of the second optical system 200 during content reproduction in thefirst recording and reading layer 14A.

As described above, the optical recording medium 10 and the opticalrecording and reading method in the present embodiment include: a servolayer using step of recording information in the group of recording andreading layers 14 while performing tracking using the servo layer 18;and a recorded area using step of recording information in another groupof recording and reading layers 14 while performing tracking usingrecorded areas of information in the recording and reading layers 14. Asa result, when information is recorded in the group of recording andreading layers 14 for the first time, tracking control is performedusing the servo layer 18 in a positive manner in the servo layer usingstep. On the other hand, if a data area of one of the recording andreading layers becomes a recorded area, the procedure proceeds to therecorded area using step. As a result, it is possible to recordinformation in other recording and reading layers while performingtracking control using the recorded area of the recording and readinglayer.

By this means, even if the number of layers in the group of recordingand reading layers 14 increases, it is possible to shorten the distancebetween the recorded areas in the group of recording and reading layers14 in which tracking control is performed and unrecorded areas in therecording and reading layers in which information is recorded (i.e.layer-direction distance). As a result, it is possible to decrease athickness tolerance occurring between the tracking control beam 270 andthe recording and reading beam 170, so that it is possible to stabilizetracking signals without performing focus control of the trackingcontrol beam 270 independently.

Especially, according to the present embodiment, in the servo layerusing step, information is recorded in the first recording and readinglayer 14A adjacent to the servo layer 18. As a result, it is possible todecrease the inter-layer distance between the servo layer 18 and thefirst recording and reading layer 14A (particularly, it is possible toset the distance equal to or less than 20 μm), so that it is possible tostabilize tracking signals. Also, even in the recorded area using step,for example, in the case of using a recorded area of the first recordingand reading layer 14A, information is recorded in the second recordingand reading layer 14B adjacent thereto. In the case of using a recordedarea of the second recording and reading layer 14B, information isrecorded in the third recording and reading layer 14C adjacent thereto.In this way, by placing a recording and reading layer for trackingcontrol and a recording and reading layer of the recording target inadjacent positions, similarly, it is possible to stabilize trackingsignals more significantly.

Further, in the present embodiment, in both the servo layer using stepand the recorded area using step, a recording operation continues untilthe recording of information is completed in the entire data area in arecording and reading layer of the recording target. It should be notedthat “continuing” means that no area in which tracking is impossible isprovided by remaining an unrecorded status in a data area of a recordingand reading layer of the recording target. Therefore, by controlling anunrecorded area not to be formed in a data area of a recording andreading layer as in the present embodiment, it is possible to providestabled tracking control to other recording and reading layers.

Also, in the present embodiment, a waveform of the tracking beam 270 anda waveform of the recording beam 170 are set to be in the same bluewavelength area and be the same wavelength. Further, in the servo layer18, a recording and reading film in which information can be recorded isformed by one of these beams 170 and 270. By using the servo layer 18effectively as a recording layer, it is possible to increase therecording capacity of the optical recording medium 10 and recordmanagement information in this servo layer 18. For example, by readingthe management information recorded in this servo layer 18 at the timeof a recording and reading start, it is possible to quickly find therecording start position and the reproducing start position in the groupof recording and reading layers 14, so that it is possible to enhancethe recording and reading efficiency.

In this optical recording medium 10, the thickness of the buffer layer17 placed between the servo layer 18 and the first recording and readinglayer 14A is substantially the same as one of the thicknesses in thegroup of intermediate layers 16. By this means, it is possible toshorten the distance between the servo layer 18 and the group ofrecording and reading layers 14 and stabilize tracking signals in theservo layer 18. Also, the distance between the servo layer 18 and thegroup of recording and reading layers 14 is shortened, so that, at thetime of making the servo layer 18 function as a recording and readinglayer, it is possible to use the first optical system 100 as is forrecording and reading in the group of recording and reading layers 14.Particularly, by the first optical system 100, it is possible tofacilitate position estimation of the servo layer 18 and to easily usethe servo layer 18 as part of the group of recording and reading layers14 in the first optical system 100.

It should be noted that, in this optical recording medium 10, tosuppress a crosstalk, two kinds of thicknesses are set for the group ofintermediate layers 16 and large and small film thicknesses arealternately set. Therefore, in the present embodiment, by setting thethickness of the buffer layer 17 to 12 μm which is the film thickness ofthe second intermediate layer 16B, the alternate relationship betweentwo kinds of thicknesses is maintained. By this means, it is arrangedsuch that the servo layer 18 does not have harmful effects when thefirst recording and reading layer 14A is reproduced.

Also, in the present embodiment, compared to the group of recording andreading layers 14, the servo layer is placed in a position furthererfrom the light incident surface in the optical recording medium 10. BYthis means, it is possible to directly form the concavo-convex pattern(i.e. the land 18A and the groove 18B) on the support substrate 12, sothat it is possible to create the servo layer 18 easily and reduce amanufacturing cost.

In the optical recording medium 10 of the present embodiment, although acase has been limitedly described where the servo layer 18 is placed ina furtherer side from the light incident surface 10A than the group ofrecording and reading layers 14, the present invention is not limited tothis. Also, although a case has been limitedly described where six ormore recording and reading layers are provided as the group of recordingand reading layers 14, the present invention is not limited to this.

FIG. 5 shows a case where, as the optical recording medium 10 accordingto other embodiments, the servo layer 18 is placed in a position closerto the side of the light incident surface 10A than the four-layer groupof recording and reading layers 14. By this means, the servo layer 18becomes close to the light incident surface 10A, so that it is possibleto enhance the expandability of an aberration correcting range andtherefore enhance the tracking accuracy. It should be noted that,although a Fig. is not shown here, it is possible to place a servo layerin the intermediate of the group of recording and reading layers.

Further, in the optical recording and reading method of the presentembodiment, a recording operation continues until the recording ofinformation is completed in the entire data area in a recording andreading layer of the recording target, in both the servo layer usingstep and the recorded area using step. However, the present invention isnot limited to this. For example, as shown in FIGS. 6A and 6B, it ispossible to divide the data area of the group of recording and readinglayers 14 into a plurality of areas E in the radius direction andperform recording every area E in the layer direction.

Also, in the optical recording and reading method of the presentembodiment, although a case has been limitedly described where the servolayer 18 in which tracking control is performed or the recorded area ofan information recording layer is always adjacent to a recording andreading layer of the recording target, the present invention is notlimited to this. For example, as shown in FIGS. 7A and 7B, it ispossible to insert other recording and reading layers between the servolayer 18 in which tracking control is performed or the recorded area ofan information recording layer and a recording and reading layer of therecording target by the beam 170. By this means, it is preferable tomaintain a certain distance (i.e. focus distance gap) between therecording and reading beam 170 and the tracking control beam 270, to theextent that the thickness tolerance is not large. As a result, theexpanding angle gap of the beams 170 and 270 becomes large, so that,even if the return light from the optical recording medium 10 is mixed,it is possible to separate it by using a slit and aperture easily. Also,as in the present embodiment, in a case where the film thicknesses ofthe group of intermediate layers 16 including the buffer layer 17 arealternately set, it is preferable to insert one recording and readinglayer between the servo layer 18 or a recorded area of an informationrecording layer and a recording and reading layer of the recordingtarget. As a result, the focus distance gap is regularly 28 μm (equal tothe sum of 16 μm and 12 μm), so that it is possible to simply set thefocus position of the tracking control beam 270.

It should be noted that, in the present embodiment, although a case hasbeen described where two kinds of inter-layer distances (16 μm and 12μm) are alternately set in the group of recording and reading layers,the present invention is not limited to this, and it is equally possibleto combine three or more kinds of inter-layer distances. Naturally, thesame film thickness may be set.

It should be noted that, although a case has been described where arecording and reading layer is filmed in advance in an optical recordingmedium to which the optical recording and reading method of theabove-noted embodiment is applied, the present invention is not limitedto this. For example, in an optical recording medium, it is equallypossible to use all of the positions of future multiple recording andreading layers as an integrated bulk layer having a predeterminedthickness. If a beam is applied to this bulk layer, only a focus part ofa beam spot has a state change and a recording mark is formed. That is,a multilayer optical recording medium of the present invention is notlimited to an optical recording medium in which a recording and readinglayer to which a beam is applied is formed in advance, and a case ispossible where recording marks are formed as needed in a planar area ofthe bulk and a plurality of recording and reading layers are provided ina later stage by multilayer formation as an aggregation of theserecording marks.

In such a case, the optical recording and reading method of the presentinvention may include: a servo layer using step of forming recordingmarks in a partial planer area of the bulk layer and forming a recordingand reading layer in a later stage while performing tracking using aservo layer; and a recorded area using step of forming recording marksin other areas of the bulk layer and forming a recording and readinglayer in a later stage while performing tracking using a recorded areaof the recording and reading layer formed in a later stage in the bulklayer. As a result of this, when information is recorded in the bulklayer for the first time, the servo layer using step performs trackingcontrol using the servo layer in a positive manner. On the other hand,once a recording and reading layer is formed in the bulk layer, theprocedure proceeds to the recorded area using step and it is possible toform recording marks in other positions while performing trackingcontrol using a recorded area in the bulk layer.

Further, although the beams 170 and 270 are in a blue wavelength rangein the present embodiment, the present invention is not limited to this.Also, for example, it is possible to set a different wavelength fromthat of the recording and reading beam 170, to the extent that the beam270 can perform tracking control using a recorded area of the group ofrecording and reading layers 14. By setting a wavelength gap between thebeams 170 and 270, it is possible to separate mixed return lights by,for example, a filter having wavelength selectivity.

Subsequently, a configuration of an optical pickup 90 used for recordingand reading is illustrated in FIG. 8 regarding a second embodiment ofthe present invention, and FIG. 9 illustrates a configuration of anoptical recording medium 10. Here, a difference from the firstembodiment will be mainly described.

A beam 270 which becomes a light source of a tracking optical system 20in the optical pickup 90 has a red wavelength of 630 to 680 nm (650 nm,here). In the optical pickup 90 in the second embodiment, the wavelengthis different between a first optical system 100 and a second opticalsystem 200, and thus, beams 170 and 270 can be separated by a filterhaving wavelength dependence.

A servo layer 18 of the optical recording medium 10 is composed byforming a reflective layer on a concavo-convex pattern (lands andgrooves) for tracking control of a support substrate 12. The recordingand reading beam 170 is set such that an amount of reflected light whenthe recording and reading beam 170 is applied to a servo layer 18becomes 5 times or less the amount of reflected light when the recordingand reading beam 170 is applied to a group of recording and readinglayers 14. As a result, when the recording and reading beam 170 isapplied to the group of recording and reading layers 14, even if thebeam 170 leaks to the servo layer 18 side, an amount of reflected lightof this leakage light in the servo layer 18 is attenuated, and aninfluence of crosstalk can be made extremely small.

Moreover, in the second embodiment, the reflectance of the servo layer18 when the recording and reading beam 170 is applied to the servo layer18 is set smaller than the reflectance when the tracking beam 270 isapplied to the servo layer 18. That is, the servo layer 18 haswavelength dependence such that the reflectance becomes higher if thered beam 270 having a long wavelength is applied, while the reflectancebecomes lower if the blue beam 170 having a short wavelength is applied.

Specifically, the reflectance of the servo layer 18 when the trackingbeam 270 is applied to the servo layer 18 is set to 40 to 95%, while thereflectance of the servo layer 18 when the recording and reading beam170 is applied to the servo layer 18 is set to 60% or less.

As a configuration example of the servo layer 18 having such opticalcharacteristics, a reflecting film (metal film) containing at least anyof Ag, Al, Au and Cu as a main component and an auxiliary film laminatedadjacently to this reflective film are provided. The reflectanceregarding the beam 270 having a long wavelength (red wavelength) can bemade high, while the reflectance regarding the beam 170 having a shortwavelength (blue wavelength) can be made low by making the refractiveindexes and the thicknesses of the reflecting film and the auxiliaryfilm different from each other. The servo layer 18 preferably has astructure of three layers or more by laminating one layer or more of thereflecting film which becomes a metal film and moreover, two layers ormore of the auxiliary film. At this time, the reflecting film islaminated on the support substrate 12 side, and the auxiliary film islaminated on top of it. For example, a three-layer structure is possiblein which the reflecting film of Ag, the auxiliary film of Si, and theauxiliary film of ZnS—SiO2 are laminated in the order from the supportsubstrate 12 side.

Furthermore, the servo layer 18 preferably has a structure of 5 layersor more by laminating two layers or more of the reflecting film andthree layers or more of the auxiliary film. At this time, at least onelayer of the auxiliary film is interposed between a first reflectingfilm and a second reflecting film. For example, a five-layer structureis preferable in which the reflecting film of Ag, the auxiliary film ofZnS—SiO2, the reflecting film of Cu, the auxiliary film of Si, and theauxiliary film of ZnS—SiO2 are laminated in the order from the supportsubstrate 12 side. With this five-layer structure, information can berecorded also in the servo layer 18. In this embodiment, the servo layer18 having the five-layer structure exemplified above is employed.

According to this servo layer 18, the reflectance of the beam 270 havinga long wavelength can be made higher and the reflectance of the beam 170having a short wavelength can be made lower.

A pitch P1 among lands 18A or grooves 18B adjacent in the servo layer 18is set to less than 0.74 μm, here. Specifically, the pitch P1 ispreferably set within a range of 0.6 to 0.7 μm or more preferably set inthe vicinity of 0.64 μm. On the other hand, a track pitch P2 ofrecording marks is set to a half (½) of the pitch P1 of the lands 18Aand the grooves 18B. That is, the track pitch P2 between the recordingmarks is set to less than 0.37 μm or preferably set within a range of0.26 to 0.35 μm or more preferably set in the vicinity of 0.32 μm. As aresult, the track pitch P2 between the recording marks becomesapproximately 0.32 μm, which is compatible with the BD standard.

The pitch P1 (approximately 0.64 μm) among the lands 18A/grooves 18B ofthe servo layer 18 is the size capable of sufficient tracking with thebeam 270 having a relatively long red wavelength range. In thisembodiment, tracking is executed by using both the lands 18A and thegrooves 18B. As a result, the track pitch P2 of the recording marksbecomes approximately 0.32 μm, which is a half of the pitch P1 of theservo layer 18. As described above, by executing tracking control byusing the lands 18A and the grooves 18B, respectively, the track pitchP2 of the recording marks of the group of recording and reading layers14 can be reduced even without reducing the pitch P1 of the servo layer18.

A buffer layer 17 is formed of a light transmitting acrylic ultravioletcurable resin. The thickness of this buffer layer 17 is preferably setto 10 to 200 μm. If the thickness of this buffer layer 17 is 10 μm orless, the servo layer 18 and the group of recording and reading layers14 become too close to each other and can give a bad effect to eachother. On the other hand, if the thickness of the buffer layer 17 is 200μm or more, uniformity of the thickness can be easily deteriorated in aprocess of forming a film of the buffer layer 17. Here, the thickness isset to 30 μm.

As a result, the servo layer 18 of the optical recording medium 10 islocated at a distance of 0.140 mm (140 μm) from a light incident surface10A.

Subsequently, a recording and reading method and its action using theoptical recording medium 10 in the second embodiment will be describedby using the optical pickup 90 by referring to FIG. 10 and after.

<Recording in Group of Recording and Reading Layers>

For example, if information is to be recorded in a first recording andreading layer 14A adjacent to the servo layer 18, first, the beam 270 ina red wavelength area of a second optical system 200 is applied to theservo layer 18 and tracking is performed. Specifically, as illustratedin FIG. 10(A), a spot of the beam 270 is applied alternately to both thegrooves 18B and the lands 18A in the servo layer 18 and tracking isperformed. At the same time as this work, the recording and reading beam170 in a blue wavelength area of a first optical system 100 is appliedto the first recording and reading layer 14A.

As a result, the information is recorded in the first recording andreading layer 14A along the grooves 18B or the lands 18A while trackingis performed for the grooves 18B and the lands 18A. At this time, a partof the recording and reading beam 170 applied to the first recording andreading layer 14A is transmitted through this first recording andreading layer 14A and reaches the servo layer 18. However, as alreadydescribed, the amount of reflected light when the recording and readingbeam 170 is applied to the servo layer 18 is set to 5 times or less theamount of reflected light when the recording and reading beam 170 isapplied to the group of recording and reading layers 14. Therefore, evenif the beam 170 passing through the first recording and reading layer14A is reflected by the servo layer 18, the light amount of thereflected light is considerably attenuated. As a result, a bad influenceon the recording mark formed on the first recording and reading layer14A can be suppressed. Moreover, the servo layer 18 sufficientlyreflects the tracking beam 270 while suppressing reflection of therecording and reading beam 170. Specifically, the reflectance of thetracking beam 270 is maintained at as high as 40 to 95% in the servolayer 18. On the other hand, the reflectance of the recording andreading beam 170 is suppressed to 60% or less. As a result, stabletracking control is realized.

Basic specifications relating to the optical recording medium 10 andinformation relating to the number of layers of the group of informationrecording layers 14 are recorded in advance in a recording pit or BCA(burst cutting area) in the servo layer 18 and read out before thetracking control is started all the time. Basic information relating tothe optical recording medium includes a rule concerning the position ofthe servo layer 18, positions of first to sixth recording and readinglayers 14A to 14F, and an inter-layer distance of the group of recordingand reading layers.

After recording of required information in the first recording andreading layer 14A has been completed, additional information (addressinformation relating to recording, contents information and the like)this time is recorded in the first recording and reading layer 14A andcompleted. After that, if the recording of information in the firstrecording and reading layer 14A is to be resumed, first, managementinformation recorded in this first recording and reading layer 14A isreproduced, the position where the previous recording is completed ischecked, and recording is continued from that position. As describedabove, information can be recorded to all the data areas in the firstrecording and reading layer 14A to the sixth recording and reading layer14F.

<Reproduction of Group of Recording and Reading Layers>

For example, if information recorded in the first recording and readinglayer 14A adjacent to the servo layer 18 is to be reproduced, first, thebeam 270 in the red wavelength area of the second optical system 200 isapplied to the servo layer 18 and tracking is performed. Specifically,as illustrated in FIG. 10(B), a spot of the beam 270 is applied to thegrooves 18B and the lands 18A in the servo layer 18 and tracking isperformed. At the same time as this work, the recording and reading beam170 in the blue wavelength area of the first optical system 100 isapplied to the first recording and reading layer 14A.

As a result, the information recorded in the first recording and readinglayer 14A is reproduced along the grooves 18B or the lands 18A whiletracking is performed for the grooves 18B and the lands 18A. At thistime, a part of the recording and reading beam 170 applied to the firstrecording and reading layer 14A is transmitted through this firstrecording and reading layer 14A and reaches the servo layer 18. However,as already described, the amount of reflected light when the recordingand reading beam 170 is applied to the servo layer 18 is set to 5 timesor less the amount of reflected light when the beam 170 is applied tothe group of recording and reading layers 14. Therefore, even if thebeam 170 passing through the first recording and reading layer 14A isreflected by the servo layer 18, the light amount of the reflected lightis considerably attenuated, and thus, crosstalk with a reading signalcan be considerably suppressed. Moreover, the servo layer 18sufficiently reflects the tacking beam 270 while suppressing thereflection of the recording and reading beam 170. Specifically, thereflectance of the tracking beam 270 is maintained at as high as 40 to95% in the servo layer 18, while the reflectance of the recording andreading beam 170 is suppressed to 60% or less. As a result, even if apart of the recording and reading beam 170 leaks out to the servo layer18, the quality of a tracking signal is not deteriorated. As describedabove, the information recorded in the data area of the first recordingand reading layer 14A to the sixth recording and reading layer 14F isreproduced.

As described above, according to the optical recording medium 10 of thisembodiment, the reflectance of the servo layer 18 when the recording andreading beam 170 is applied to the servo layer 18 is set smaller thanthe reflectance when the recording and reading beam 170 is applied tothe group of recording and reading layers 14. As a result, when therecording and reading beam 170 is applied to the group of recording andreading layers 14, even if a part thereof leaks out to the servo layer18 on the depth side, the amount of reflected light of the servo layer18 is made small, and a bad influence on a recording and readingoperation can be avoided.

Moreover, in this embodiment, since the amount of reflected light whenthe recording and reading beam 170 is applied to the servo layer 18 isset to 5 times or less the amount of reflected light when the recordingand reading beam 170 is applied to the group of recording and readinglayers 14. As a result, even if the recording and reading beam 170applied to the group of recording and reading layers 14 leaks out to theservo layer 18 on the depth side, most of the beam is absorbed ortransmitted by this servo layer 18.

On the other hand, in this optical recording medium 10, the reflectancewhen the recording and reading beam 170 is transmitted through the groupof recording and reading layers 14 and applied to the servo layer 18 isset smaller than the reflectance when the tracking beam 270 is passedthrough the group of recording and reading layers 14 and applied to theservo layer 18. By employing this servo layer 18, the tracking beam 270is sufficiently reflected while the reflection of the recording andreading beam 170 is suppressed, and thus, quality deterioration of thetracking signal can be prevented.

Particularly in this embodiment, since the optical characteristics ofthe servo layer 18 are changed depending on the wavelength as describedabove, the servo layer has a structure in which a reflecting film (metalfilm) having a metal material as a main component and an auxiliary filmhaving refractive index and film thickness different from those of thisreflecting film are laminated. By configuring as such, reflected lightintensity of a specific wavelength (a blue wavelength, here) notrequired in tracking can be optically reduced.

Moreover, as the result of the configuration of the optical recordingmedium 10 as above, the inter-layer distance between the group ofrecording and reading layers 14 and the servo layer 18 can be made smallto 10 to 200 μm, and the number of layers of the group of recording andreading layers 14 can be increased.

Subsequently, by referring to FIGS. 11(A) and 11(B), an opticalrecording medium 310 according to a third embodiment will be described.Regarding this optical recording medium 310, the same or the similarportions as those in the optical recording medium 10 in the secondembodiment are given the same last two digits in the reference numeralsin the drawings and the description, and description of the individualmembers are omitted and only differences will be mainly described.

This optical recording medium 310 includes a cover layer 311, a group ofrecording and reading layers 314 and a group of intermediate layers 316,a buffer layer 317, a servo layer 318, and a support substrate 312 fromthe side of a light incident surface 310A.

The servo layer 318 includes a single layer of a metal film containingat least any of Ag, Al, Au, and Cu as a main component. Therefore, anauxiliary film is not provided.

The buffer layer 317 is provided between the servo layer 318 and thegroup of recording and reading layers 314 and is formed of a materialobtained by kneading a dye or uniformly dissolving it in a lighttransmitting resin. Specifically, the buffer layer 317 employs amaterial having lower absorbance of a first wavelength (650 nm, here) ofthe tracking beam 170 and higher absorbance of a second wavelength (405nm, here) of the recording and reading beam 270 and functions as afilter layer having wavelength dependence. Here, a material in which ageneral dye having a chromophore and an auxochrome which become yellowas azo, diazo, and azomethine is dispersed in or bonded to a transparentresin is used.

According to this optical recording medium 310, even if the recordingand reading beam 170 applied to the group of recording and readinglayers 314 leaks out to the servo layer 318 side, this leakage light isabsorbed by the buffer layer 317 before it reaches the servo layer 318.Moreover, even if this leakage light is reflected by the servo layer318, the reflected light is absorbed by the buffer layer 317 again.

Moreover, this optical recording medium 310 is set such that thereflectance when the recording and reading beam 170 is applied issmaller than the reflectance when the tracking beam 270 is applied tothe servo layer 318. That is because the recording and reading beam 170is absorbed by the buffer layer 317 before reaching the servo layer 318.

As a result, with this optical recording medium 310, the quality of boththe reading signal and tracking signal can be improved. Moreover, withthis optical recording medium 310, the buffer layer 317 is arranged onthe side deeper than the group of recording and reading layers 314. As aresult, external lightsuch as ultraviolet rays causing the dye materialbleached is absorbed by the group of recording and reading layers 314 onthe front side and does not reach the buffer layer 317 easily.Therefore, long-term stability of the buffer layer 317 is ensured, andtemporal deterioration of the optical recording medium 310 can besuppressed. Particularly if an organic dye is to be employed, aninfluence of the ultraviolet rays is large, and thus, the structure ofthis optical recording medium 310 is preferable.

In this embodiment, the example in which the buffer layer 317 uses amaterial having such wavelength dependence that the absorptance ortransmittance is different depending on the wavelength band isexemplified, but as illustrated in FIGS. 12(A) and 12(B), for example, afilter layer 317B may be arranged separately from the buffer layer 317,and the wavelength dependence may be added to the filter layer 317B bykneading a dye in a light transmitting resin of this filter layer 317B.

Next, an optical recording medium 410 according to a fourth embodimentwill now be described with reference to FIG. 13. Concerning the opticalrecording medium 410, parts similar or identical to those of the opticalrecording medium 10 described in the second embodiment will bedesignated with reference numerals having the same last two digits inthe following drawings and description, and thereby, a description ofeach member will be omitted and different respects will be mainlydescribed.

The optical recording medium 410 includes, starting with a first surface410A, a first cover layer 411, a first group of recording and readinglayers 414 and first group of intermediate layers 416, a first bufferlayer 417, a servo layer 418, a support substrate 412, a second bufferlayer 437, a second group of recording and reading layers 434 and secondgroup of intermediate layers 436, a second cover layer 431, and a secondsurface 430A in this order. That is, the optical recording medium 410 isdifferent from the optical recording medium 10 of the first embodimentin that the optical recording medium 410 includes the second bufferlayer 437, the second group of recording and reading layers 434 andsecond group of intermediate layers 436, and the second cover layer 431also at the second surface 430A side with respect to the supportsubstrate 412.

The support substrate 412 has a thickness set at 900 μm, and at thefirst surface 410A, lands 418A and grooves 418B are spirally formed froman area close to the center to an outer edge.

The servo layer 418 includes a single layer of metal film mainlycomposed of at least one of Ag, Al, Au, and Cu. Thus, the servo layer418 does not include an auxiliary film. A pitch P1 between the lands418A or between the grooves 418B of the servo layer 418 is set at around0.64 μm. On the other hand, a track pitch P2 between recording marks isset at a half (½) of the pitch P1 between the lands 418A or between thegrooves 418B. Specifically, the track pitch P2 between the recordingmarks is set at around 0.32 μm. As a result, the track pitch P2 betweenthe recording marks is around 0.32 μm, which is compatible with a BDstandard.

In the present embodiment, tracking is performed by using both the land418A and the groove 418B. As a result, the track pitch P2 between therecording marks is around 0.32 μm, which is a half of the pitch P1 ofthe servo layer 418.

The first buffer layer 417 has a film thickness set at 30 to 40 μm andis composed of a material obtained by dispersing or combining dye intoor with light transmitting resin through mixing or homogeneousdissolving. Specifically, for the first buffer layer 417, a material isadopted in which the absorbance of a first wavelength (here, 650 nm) tobe a tracking beam is low and the absorbance of a second wavelength(here, 405 nm) to be a recording and reading beam is high. Herein, anadopted material is one obtained by dispersing or combining common dyehaving chromophores and auxochromes that give yellow such as azo, diazo,and azomethine, into or with transparent resin.

The first cover layer 411 is composed of optically transparent acrylicultraviolet curable resin and has a film thickness set at 40 μm.

The second buffer layer 437 has a film thickness set at 20 to 40 μm andis composed of a material obtained by mixing or homogeneously dissolvingdye into or with light transmitting resin. Specifically, for the secondbuffer layer 437, a material is adopted in which the absorbance of afirst wavelength (here, 650 nm) to be a tracking beam is low and theabsorbance of a second wavelength (here, 405 nm) to be a recording andreading beam is high. Herein, an adopted material is one obtained bydispersing or combining common dye having chromophores and auxochromesthat give yellow such as azo, diazo, and azomethine, into or withtransparent resin.

The second group of recording and reading layers 434 (L0 to L5 recordingand reading layers 434A to 434F) and the second group of intermediatelayers 436 stacked at the second surface 430A side of the second bufferlayer 437 have substantially the same structure as those of the firstgroup of recording and reading layers 414 and the second group ofintermediate layers 416.

The second cover layer 431 is composed of optically transparent acrylicultraviolet curable resin and has a film thickness set at 40 μm.

As a result of such structure, a boundary (the servo layer 418) betweenthe support substrate 412 and the first buffer layer 417 in the opticalrecording medium 410 is located at a distance of about 150 μm from thefirst surface 410A. An L0 recording and reading layer 414A farthest fromthe first surface 410A in the first group of recording and readinglayers 414 is located at a distance of 112 nm from the first surface410A, an L1 recording and reading layer 414B is located at a distance of96 μm from the first surface 410A, an L2 recording and reading layer414C is located at a distance of 84 μm from the first surface 410A, anL3 recording and reading layer 414D is located at a distance of 68 μmfrom the first surface 410A, an L4 recording and reading layer 414E islocated at a distance of 56 μm from the first surface 410A, and an L5recording and reading layer 414F closest to the first surface 410A islocated at a distance of 40 μm from the first surface 410A. Also, atotal thickness of the first group of recording and reading layers 414(a distance between the L0 recording and reading layer 414A to the L5recording and reading layer 414F) is 72 μm.

Also, the L0 recording and reading layer 434A farthest from the secondsurface 430A in the second group of recording and reading layers 434 islocated at a distance of 112 μm from the second surface 430A, the L1recording and reading layer 434B is located at a distance of 96 μm fromthe second surface 430A, the L2 recording and reading layer 434C islocated at a distance of 84 μm from the second surface 430A, the L3recording and reading layer 434D is located at a distance of 68 μm fromthe second surface 430A, the L4 recording and reading layer 434E islocated at a distance of 56 μm from the second surface 430A, and the L5recording and reading layer 434F closest to the second surface 430A islocated at a distance of 40 μm from the second surface 430A. Also, atotal thickness of the second group of recording and reading layers 434(a distance between the L0 recording and reading layer 434A to the L5recording and reading layer 434F) is 72 μm.

The optical recording medium 410 is symmetrical in the thicknessdirection, except for the servo layer 418. As a result, because internalstress generated when the optical recording medium 410 is manufacturedis symmetrical in the thickness direction, warpage and deformation canbe reduced. In particular, even if a thickness of the support substrate412 is reduced to 600 μm or less, e.g., 100 μm, amounts of warpage anddeformation of the optical recording medium 410 can be lowered.

FIG. 14 illustrates configurations of first and second optical pickups90A and 90B used for the recording and reading of the optical recordingmedium 410 according to the fourth embodiment. The first optical pickup90A applies a beam to the first surface 410A, which is one side of theoptical recording medium 410. The second optical pickup 90B applies abeam to the second surface 430A, which is the other side of the opticalrecording medium 410. It should be noted that internal configurations ofthe first and second optical pickups 90A and 90B are substantially thesame as that of the optical pickup 90 illustrated in the firstembodiment, so that in the following drawings and description, A isadded to each end of reference numerals at the side of the first opticalpickup 90A, and B is added to each end of reference numerals at the sideof the second optical pickup 90B. Thereby, an illustration and adescription thereof will be omitted.

The first optical pickup 90A includes a recording and reading opticalsystem 100A and a tracking optical system 200A. The recording andreading optical system 100A is an optical system that applies arecording and reading beam 170A to the first group of recording andreading layers 414 of the optical recording medium 410 to performrecording and reading. The tracking optical system 200A is an opticalsystem that applies a tracking beam 270A to the servo layer 418 toperform tracking control when the recording and reading optical system100A is used to record information on the first group of recording andreading layers 414.

The second optical pickup 90B includes a recording and reading opticalsystem 100B and a tracking optical system 200B. The recording andreading optical system 100B is an optical system that applies arecording and reading beam 170B to the second group of recording andreading layers 434 of the optical recording medium 410 to performrecording and reading. The tracking optical system 200B is an opticalsystem that applies a tracking beam 270B to the servo layer 418 toperform tracking control when the recording and reading optical system100B is used to record information on the second group of recording andreading layers 434.

Next, a method for recording and reading information on the opticalrecording medium 410 will be described with reference to the first andsecond optical pickups 90A and 90B.

<Recording/Reading on a First Group of Recording and Reading Layers>

For example, if recording and reading of information is performed on theL0 recording and reading layer 414A of the first group of recording andreading layers 414, first, the tracking beam 270A in a red wavelengthrange from the first optical pickup 90A is applied to the servo layer 18to perform tracking Specifically, as illustrated in FIG. 13, a spot ofthe tracking beam 270A is applied to the groove 418B and the land 418Ain the servo layer 418 to perform tracking.

Simultaneously therewith, the recording and reading beam 170A in a bluewavelength range from the first optical pickup 90A is applied to the L0recording and reading layer 414A, and thereby recording or reading isperformed on the L0 recording and reading layer 414A.

At this time, even if the recording and reading beam 170A applied to thefirst group of recording and reading layers 414 leaks to the side of theservo layer 418, the beam is absorbed by the first buffer layer 417before the leakage light reaches the servo layer 418. Also, even if theleakage light is reflected by the servo layer 418, the reflected lightis absorbed by the first buffer layer 417 again. Also, the first bufferlayer 417 actively transmits the tracking beam 270A in the redwavelength to increase an amount of light of tracking signals. As aresult, stable tracking control is provided.

<Recording/Reading on a Second Group of Recording and Reading Layers>

If information is recorded on the L0 recording and reading layer 434A ofthe second group of recording and reading layers 434, first, thetracking beam 270B in the red wavelength range from the second opticalpickup 90B is applied to the servo layer 418 through the supportsubstrate 412 to perform tracking. Specifically, as illustrated in FIG.13, a spot of the tracking beam 270B is applied to the land 18A and thegroove 418B in the servo layer 418 to perform tracking. Simultaneouslytherewith, the recording and reading beam 170B in a blue wavelengthrange from the second optical pickup 90B is applied to the L0 recordingand reading layer 434A, and thereby recording or reading is performed onthe L0 recording and reading layer 434A.

At this time, even if the recording and reading beam 170B applied to thesecond group of recording and reading layers 434 leaks to the side ofthe servo layer 418, the beam is absorbed by the second buffer layer 437before the leakage light reaches the servo layer 418. Also, even if theleakage light is reflected by the servo layer 418, the reflected lightis absorbed by the second buffer layer 437 again. Also, the secondbuffer layer 437 actively transmits the tracking beam 270B in the redwavelength to increase an amount of light of tracking signals. As aresult, stable tracking control is provided.

It should be noted that simultaneous recording or reading may also beperformed on the first group of recording and reading layers 414 and thesecond group of recording and reading layers 434. This doubles atransfer rate of recording or reading.

As hereinbefore discussed, according to the optical recording medium 410of the fourth embodiment, the servo layer 418 is formed on one surfaceof the support substrate 412, and the first group of recording andreading layers 414 and the second group of recording and reading layers434 are disposed on both surfaces of the support substrate 412. As aresult, because internal stress generated when the first and secondgroups of recording and reading layers 414 and 434 are formed isdispersed into both sides of the support substrate 412, warpage anddeformation of the optical recording medium 410 can be prevented. Suchdispersion of internal stress enables preventing warpage of the opticalrecording medium 410 even if a thickness of the support substrate 12 isset within the range of 10 to 1000 μm, and preferably, within the rangeof 10 to 600 μm.

At this time, an attempt to form concavo-convex patterns for tracking onboth sides of the support substrate 412 complicates a process formanufacturing the support substrate 412, so that the accuracy of thesupport substrate 412 tends to be deteriorated. For this reason, in thepresent embodiment, the accuracy is improved by forming concavo-convexpatterns for tracking on one surface of the support substrate 412 tosimplify the manufacture of the support substrate 412. Also, because theservo layer 418 is shared by the first and second groups of recordingand reading layers 414 and 434, which sandwich the servo layer 418,concavo-convex patterns for tracking are not needed to be formed on boththe recording and reading layers of the first and second groups ofrecording and reading layers 414 and 434. As a result, the geometricaccuracy of the optical recording medium 410 can be more improved. Sincethe first group of recording and reading layers 414 and the second groupof recording and reading layers 434 are disposed at both sides of thesupport substrate 412, a recording capacity may also be increased.

Further, in the optical recording medium 410, the reflectance of theservo layer 418 to the tracking beams 270A and 270B in the redwavelength is set to be greater than that to the recording and readingbeams 170A and 170B. In order to embody this, a material used for thefirst and second buffer layers 417 and 437 has a larger amount ofabsorbed light with the shortness of a beam wavelength. Then, even ifthe recording and reading beams 170A and 170B in the blue wavelength areincident on the side of the servo layer 18, the incident beams areabsorbed by the first and second buffer layers 417 and 437, so that anamount of leakage light that reaches the servo layer 418 and an amountof reflected light from the servo layer 418 can be reduced. On the otherhand, since the tracking beams 270A and 270B in the red wavelength canbe actively transmitted through the first and second buffer layers 417and 437, an amount of reflected light from the servo layer 418 can beincreased. As a result, crosstalk between the recording and readingbeams 170A, 170B and the tracking beams 270A, 270B is reduced, thequality of reading signals is improved, as well as stable trackingcontrol is provided.

Also, as shown herein, lowered reflectance of the servo layer 418 to therecording and reading beams 170A and 170B results in possible reducedthicknesses of the first and second buffer layers 417 and 437. In thepresent embodiment, specifically, the thicknesses may be reduced topreferably 200 μm or less, desirably 100 μm or less, and more desirably50 μm or less. If the thicknesses of the first and second buffer layers417 and 437 may be reduced in this manner, a film thickness erroroccurring when the first and second buffer layers 417 and 437 aredeposited may be small accordingly. Additionally, since the supportsubstrate 412 may be thicker, warpage generated while the opticalrecording medium 410 is being manufactured can be more reduced.

Further, in the optical recording medium 410, thicknesses of the firstbuffer layer 417 and the second buffer layer 437 are set to besubstantially the same. As a result, warpage in the support substrate412 generated while the first and second buffer layers 417 and 437 arebeing formed can be prevented. That is, the support substrate 412 may bethinner or formed of a low-rigidity material, and the layer number ofthe first group of recording and reading layers 414 and the second groupof recording and reading layers 434 may be larger accordingly.

Also, the first group of recording and reading layers 414 and the secondgroup of recording and reading layers 434 of the optical recordingmedium 410 are stacked symmetrically with respect to the center of thesupport substrate 412 in the thickness direction. Therefore, internalstress generated in the first and second groups of recording and readinglayers 414 and 434 is also symmetrical, so that warpage of the opticalrecording medium 410 can be prevented.

When the optical recording medium 410 of the fourth embodiment ismanufactured, it is preferable to simultaneously form, at both sides,the first buffer layer 417 and the second buffer layer 437, the firstgroup of recording and reading layers 414 and the second group ofrecording and reading layers 434, and the first group of intermediatelayers 416 and the second group of intermediate layers 436. As a result,because internal stress generated at the time of ultraviolet curing actsevenly on both sides of the support substrate 412, warpage of theoptical recording medium 410 can be more reduced.

In the fourth embodiment, the first and second buffer layers 417 and 437have characteristics that light absorptivities are different between thered and blue wavelengths, resulting in different reflectances of theservo layer 418 between the tracking beam and the recording and readingbeam, but the present invention is not limited thereto. For example, areflecting film itself formed on the servo layer 418 may have wavelengthdependence that reflectance is dependent on a wavelength. Also, inaddition to the first and second buffer layers 417 and 437, a filterlayer having wavelength dependence of optical transmittance andabsorptance may be formed. Further, a substrate material may havewavelength dependence.

For the purpose of simply checking the characteristics of the opticalrecording medium 10 of the first embodiment, this optical recordingmedium was actually fabricated and evaluations were made using anoptical disc industry-standard optical disc measuring device ETA-optic(made by Steag ETA-Optik GmbH in Germany) having functions of acommonly-used spectrometer. Specifically, measurements were made of thereflectance of the servo layer of this optical recording medium near a405 nm wavelength of a recording and reading laser diode and near a 650nm wavelength of a tracking laser diode. As a result, reflectance at ablue wavelength (405 nm) was 9% and reflectance at a red wavelength (650nm) was 52%. Thus, it was confirmed that the reflectance of the servolayer was lower when light having the wavelength of a recording andreading beam was applied to the servo layer than when light having thewavelength of a tracking beam was applied to the servo layer.

In addition, a disc for calculation in which respective metal films andauxiliary films of the servo layer were not formed (transparent servolayer) was fabricated separately, and reflectance evaluations were madein the same way, in order to examine the reflectance of this servo layerin more detail. The reflectance characteristic of the servo layer's owncan be analyzed by detecting a difference in reflectance between thisdisc for calculation and the abovementioned regular optical recordingmedium. Reflectance measurement using this disc for calculation showedthat the reflectance was 14% for the blue wavelength (405 nm) and 32%for the red wavelength (650 nm). Yet additionally, calculation of anoptical difference (this is not a simple subtraction but means anoptical difference on the assumption of various conditions) between theregular optical recording medium and the disc for calculation showedthat a reflectance component obtained from the servo layer itself was 1%or smaller for the blue wavelength and approximately 20% for the redwavelength. That is, it was confirmed that reflectance for thewavelength of the tracking beam was significantly lower than reflectancefor the wavelength of the recording and reading beam with regard toreflection from the servo layer in an actual optical recording medium.

Next, there were fabricated samples, as optical recording mediumsaccording to Practical Examples 1 and 2, in which the group of recordingand reading layers 14 of the optical recording medium 10 shown in thefirst embodiment was decreased in the number of layers to a singlelayer, in order to make further verifications under conditions close toactual signal processing characteristics. That is, these opticalrecording mediums 10 were configured to include a cover layer 11, arecording and reading layer 14, a buffer layer 17, a servo layer 18, anda support substrate 12, as illustrated in FIG. 15.

Note that a servo layer 18 of Practical Example 1 employed a 5-layerstructural film in which an Ag reflecting film, a ZnS—SiO₂ auxiliaryfilm, a Cu reflecting film, an Si reflecting film, and a ZnS—SiO₂auxiliary film were stacked. The overall film thickness of the servolayer was set to 119 nm. Note that the total thickness of the Agreflecting film and the Cu reflecting film, among the abovementionedfilms, was set to 91 nm. In addition, in Practical Example 1, thethickness of the buffer layer 17 was set to 30 μm. In Practical Example2, the thickness of other auxiliary films was changed, while the totalthickness of the Ag reflecting film and the Cu reflecting film of theservo layer 18 was also set to 91 nm. In addition, the thickness of thebuffer layer 17 was also changed to 40 μm.

In addition, there was fabricated a sample, as an optical recordingmedium according to Practical Example 3, in which the group of recordingand reading layers 14 of the optical recording medium 310 shown in thesecond embodiment was decreased in the number of layers to a singlelayer. A servo layer 18 of this Practical Example 3 employed an 80nm-thick single-layer Ag alloy metal film. For a buffer layer 17, therewas used a material prepared by mixing a commonly-known dye havingyellow chromophore and auxochrome, such as an azo skeleton, with theabovementioned transparent acrylic resin material. This material wasadapted to be low in absorbance for the first wavelength (650 nm here)of the tracking beam 170, and high in absorbance for the secondwavelength (405 nm here) of the recording and reading beam 270.

Note that in all of Practical Examples 1 to 3, the recording and readinglayer 14 was formed using Bi—Ge—O as the material thereof. In addition,lands 19A and grooves 19B for signal quality evaluation were purposelyformed on the recording and reading layer 14, in order to evaluatereading signals of the recording and reading layer 14. Accordingly,there was adopted a method of indirectly evaluating the quality of areading signal by evaluating the quality of a tracking signal usingthese lands 19A and grooves 19B.

On the other hand, there were fabricated optical recording mediums, asthose of Comparative Examples 1 to 3, in which a light absorptionfunction was not added to the buffer layer 17, and a metallicsingle-layer film was employed for the servo layer 18. The servo layer18 of Comparative Example 1 was formed of an 80 nm-thick Ag alloy metalfilm; the servo layer 18 of Comparative Example 2 was formed of a 20nm-thick Ag alloy metal film; and the servo layer 18 of ComparativeExample 3 was formed of 10 nm-thick Ag alloy metal film.

As a method of evaluating respective optical recording mediums, arecording and reading beam 170 having a blue wavelength was applied tothe recording and reading layer 14, reflected light containing atracking signal of lands 19A or grooves 19B was detected by an opticaldetector 132 as voltage variation, and a determination was made onwhether or not tracking control was possible and on the amount of noisein the tracking signal. If the lands 19A or the grooves 19B can betracked using the tracking signal contained in the reflected light ofthe recording and reading layer 14, the quality of the reading signal ofthe recording and reading layer 14 can be estimated to be satisfactory.Likewise, if the amount of noise contained in this tracking signal issmall, the quality of the reading signal can also be estimated to besatisfactory. Note that part of the recording and reading beam 170having a blue wavelength applied to the recording and reading layer 14leaks out to the servo layer 18 side. If this leakage light stronglyreflects on the servo layer 18, the amount of noise contained in thetracking signal increases.

For reference, the amount of reflected light when the recording andreading beam 170 was applied to the recording and reading layer 14 andthe amount of reflected light when this recording and reading beam 170was directly applied to the servo layer 18 were examined, and a ratiobetween the two amounts was evaluated. In addition, the recording andreading beam 170 having a blue wavelength (405 nm) and the tracking beam270 having a red wavelength (650 nm) were applied to the servo layer 18to examine the reflectance of each beam, and the reflectance wasevaluated at three levels, i.e., “high,” “medium,” and “low.” Note thatan optical disc tester ODU 1000 which was an optical discindustry-standard tester made by Pulstec Industrial Co., Ltd. was usedas evaluation equipment.

FIG. 15 shows the results of evaluations made as described above. InPractical Example 1, the amount of reflected light when the recordingand reading beam 170 was applied to the servo layer 18 was 74.0 mV, andthe amount of reflected light when the recording and reading beam 170was applied to the recording and reading layer 14 was 84.5 mV. Thus, theratio of the amount of reflected light of the servo layer 18 to theamount of reflected light of the recording and reading layer 14 was 0.9.In addition, tracking using this reflected light (tracking signal) wassatisfactory, and the amount of noise contained in this tracking signalwas small. Note that reflectance when the recording and reading beam 170having a blue wavelength (405 nm) was applied to the servo layer 18 waslow, and reflectance when the tracking beam 270 having a red wavelength(650 nm) was applied to the servo layer 18 was high.

In Practical Example 2, the amount of reflected light when the recordingand reading beam 170 was applied to the servo layer 18 was 112.0 mV, andthe amount of reflected light when the recording and reading beam 170was applied to the recording and reading layer 14 was 160.0 mV. Thus,the ratio of the amount of reflected light of the servo layer 18 to theamount of reflected light of the recording and reading layer 14 was 0.7.In addition, tracking using this reflected light (tracking signal) wassatisfactory, and the amount of noise contained in this tracking signalwas extremely small. Note that reflectance when the recording andreading beam 170 having a blue wavelength (405 nm) was applied to theservo layer 18 was low, and reflectance when the tracking beam 270having a red wavelength (650 nm) was applied to the servo layer 18 washigh.

In Practical Example 3, the amount of reflected light when the recordingand reading beam 170 was applied to the servo layer 18 was 740.0 mV, andthe amount of reflected light when the recording and reading beam 170was applied to the recording and reading layer 14 was 160.5 mV. Thus,the ratio of the amount of reflected light of the servo layer 18 to theamount of reflected light of the recording and reading layer 14 was 4.5.In addition, tracking using this reflected light (tracking signal) wassatisfactory, and the amount of noise contained in this tracking signalwas small. Note that reflectance when the recording and reading beam 170having a blue wavelength (405 nm) was applied to the servo layer 18 waslow, and reflectance when the tracking beam 270 having a red wavelength(650 nm) was applied to the servo layer 18 was high. From this PracticalExample 3, it is understood that signal quality can be maintainedsatisfactorily if the ratio of the amount of reflected light of theservo layer 18 to the amount of reflected light of the recording andreading layer 14 is no higher than 5. In addition, from PracticalExamples 1 and 2, it is understood that signal quality can be maintainedextremely satisfactorily if this ratio is no higher than 1.

In Comparative Example 2, the amount of reflected light when therecording and reading beam 170 was applied to the servo layer 18 was5000.0 mV, and the amount of reflected light when the recording andreading beam 170 was applied to the recording and reading layer 14 was216.0 mV. Thus, the ratio of the amount of reflected light of the servolayer 18 to the amount of reflected light of the recording and readinglayer 14 was 23.1. In addition, tracking using this reflected light(tracking signal) was poor, and the amount of noise contained in thistracking signal was extremely large. Note that reflectance when therecording and reading beam 170 having a blue wavelength (405 nm) wasapplied to the servo layer 18 was high, and reflectance when thetracking beam 270 having a red wavelength (650 nm) was applied to theservo layer 18 was also high.

In Comparative Example 2, the amount of reflected light when therecording and reading beam 170 was applied to the servo layer 18 was1615.0 mV, and the amount of reflected light when the recording andreading beam 170 was applied to the recording and reading layer 14 was216.0 mV. Thus, the ratio of the amount of reflected light of the servolayer 18 to the amount of reflected light of the recording and readinglayer 14 was 19.7. In addition, tracking using this reflected light(tracking signal) was poor, and the amount of noise contained in thistracking signal was extremely large. Note that reflectance when therecording and reading beam 170 having a blue wavelength (405 nm) wasapplied to the servo layer 18 was medium, and reflectance when thetracking beam 270 having a red wavelength (650 nm) was applied to theservo layer 18 was also medium.

In Comparative Example 3, the amount of reflected light when therecording and reading beam 170 was applied to the servo layer 18 was930.0 mV, and the amount of reflected light when the recording andreading beam 170 was applied to the recording and reading layer 14 was174.5 mV. Thus, the ratio of the amount of reflected light of the servolayer 18 to the amount of reflected light of the recording and readinglayer 14 was 5.3. In addition, tracking using this reflected light(tracking signal) was possible, but the amount of noise contained inthis tracking signal was extremely large. Note that reflectance when therecording and reading beam 170 having a blue wavelength (405 nm) wasapplied to the servo layer 18 was extremely low, and reflectance whenthe tracking beam 270 having a red wavelength (650 nm) was applied tothe servo layer 18 was also low. That is, from comparison betweenPractical Example 3 and Comparative Example 3, it is understood thatsignal quality degrades, as in Comparative Example 3, if the ratio ofthe amount of reflected light of the servo layer 18 to the amount ofreflected light of the recording and reading layer 14 exceeds 5. It isalso understood that signal quality is satisfactory, as in PracticalExample 3, if the ratio is no higher than 5.

Note that a signal waveform shown in the lower section of an on-screenoutput image in FIG. 17A is the tracking signal in Practical Example 1.It is understood from the image that the tracking signal contains only asmall noise component and is extremely superior in signal quality. Onthe other hand, a signal waveform shown in the lower section of anon-screen output image in FIG. 17B is the tracking signal in ComparativeExample 1. It is understood from the image that the tracking signalcontains a large noise component and is inferior in signal quality.

In the present embodiment, cases have been shown in which the wavelengthof a tracking beam is in a red band, and the wavelength of a recordingand reading beam is in a blue band. The present invention is not limitedto these beams, however, beams having other wavelength ranges may beadopted.

In the embodiments described heretofore, there have been shown onlythose cases in which recording films are formed previously as therespective recording and reading layers. The present invention is notlimited to these cases, however. For example, like the optical recordingmedium 510 illustrated in FIG. 11, the entire area of a location whichcan be a future group of recording and reading layers may be formed intothe bulk layer 513 having a predetermined thickness. Applying arecording beam 170 to this bulk layer 513 causes only the focused partof a beam spot to undergo a state change, thus forming recording marks.That is, the optical recording medium in the present invention is notlimited to one in which recording and reading layers to be irradiatedwith a beam are previously formed. The present invention also includes acase in which recording marks are formed in a planar area as necessary,and the group of recording and reading layers 514 ismultilayer-structured, in an ex-post manner, as a set of these recordingmarks. By adopting the structure of the bulk layer 513 in the opticalrecording medium 510, it is possible to freely set the position of therecording and reading layers, as long as the position falls within therange of the bulk layer 513. The same bulk structure can also be adoptedin the optical recording medium 410 shown in the third embodiment.

Next, a fifth embodiment of the present invention will be described withreference to the accompanying drawings.

FIG. 19 illustrates an optical recording medium 10 to which an opticalrecording and reading method according to the fifth embodiment of thepresent invention is applied, and the internal configuration of anoptical recording and reading apparatus 70 for realizing this opticalrecording and reading method. This optical recording and readingapparatus 70 is provided with first and second optical pickups 90A and90B; first and second linear motion mechanisms 75A and 75B for movingthese first and second optical pickups 90A and 90B in a trackingdirection; a tracking control device 80 for controlling these first andsecond linear motion mechanisms 75A and 75B; and an output controldevice 86 for controlling the output power of respective beams of thesefirst and second optical pickups 90A and 90B.

The first and second linear motion mechanisms 75A and 75B are so-calledliner motors, on which the first and second optical pickups 90A and 90Bare mounted. As a result, the first optical pickup 90A is moved in aradial direction of the optical recording medium 10 by the first linearmotion mechanism 75A. Likewise, the second optical pickup 90B is movedin a radial direction of the optical recording medium 10 by the secondlinear motion mechanism 75B.

The first optical pickup 90A emits a beam from the first surface 10Aside of the optical recording medium 10. The second optical pickup 90Bemits a beam from the second surface 30A side of the optical recordingmedium 10. Note that the first optical pickup 90A and the second opticalpickup 90B are disposed in a state of being displaced from each other bya predetermined angular difference in the circumferential direction ofthe optical recording medium 10, though this is not illustrated inparticular. Such a way of disposal makes it possible to prevent beams ofthe respective pickups from interfering with each other. This angulardifference is preferably adjusted to, for example, no larger than 20degrees.

The internal configurations of the first and second optical pickups 90Aand 90B are substantially the same in some parts but different in otherparts. Accordingly, for components and members common to the respectivepickups, each reference numeral in figures or text is suffixed with A inthe case of the first optical pickup 90A and is suffixed with B in thecase of the second optical pickup 90B. Thus, the components andmaterials are the same in reference number except the suffixes. Here,the internal configuration of the first optical pickup 90A will bedescribed in detail, whereas the second optical pickup 90B will bedescribed with a focus on differences thereof from the first opticalpickup 90A.

As illustrated in FIG. 20, the first optical pickup 90A is provided witha recording and reading optical system 100A and a tracking opticalsystem 200A. The recording and reading optical system 100A serves as anoptical system for performing recording and reading on a first group ofrecording and reading layers 14 of the optical recording medium 10. Thetracking optical system 200A serves as an optical system for performingtracking control using a servo layer 18 when information is recorded onthe first group of recording and reading layers 14 by using therecording and reading optical system 100A.

A divergent recording and reading beam 170A emitted from a light source101A of the recording and reading optical system 100A transmits througha collimating lens 153A provided with spherical aberration correctingmeans 193A, and enters a polarizing beam splitter 152A. Note that thebeam 170A has a blue wavelength of 380 to 450 nm (405 nm here). The beam170A having entered the polarizing beam splitter 152A transmits throughthis polarizing beam splitter 152A, and is converted to circularlypolarized light as the result of further transmitting through aquarter-wave plate 154A. Thereafter, the beam 170A enters a beamsplitter 260A of the tracking optical system 200A. This beam splitter260A is set so as to be large in transmittance and small in reflectance.Specifically, the beam splitter 260A is set so that a ratio oftransmittance to reflectance is 10 or higher. Accordingly, the beam 170Atransmits through the beam splitter 260A and is converted to aconvergent beam by an objective lens 156A. This beam 170A is condensedonto either the first group of recording and reading layers 14 or theservo layer 18 formed within the optical recording medium 10 serving asan object of recording and reading.

The opening of the objective lens 156A is restricted by an aperture155A, so that a numerical aperture NA is 0.70 to 0.90 (0.85 here). Forexample, the beam 170A reflected on the first group of recording andreading layers 14 transmits through the objective lens 156A, the beamsplitter 260A and the quarter-wave plate 154A, and is converted tolinearly polarized light different by 90 degrees in phase from the beam170A on an outward path. Thereafter, the beam 170A is reflected by thepolarizing beam splitter 152A.

The beam 170A reflected by the polarizing beam splitter 152A transmitsthrough a condenser lens 159A, and is converted to converging light.Then, the beam 170A goes through a cylindrical lens 157A and enters anoptical detector 132A. Astigmatism is imparted to the beam 170A when thebeam transmits through the cylindrical lens 157A.

The optical detector 132A includes unillustrated four light-receivingunits, each of which outputs a current signal corresponding to theamount of light received. From these current signals, there aregenerated a focus error (hereinafter abbreviated as FE) signal based onan astigmatic method, a tracking error (hereinafter referred to as TE)signal based on a push-pull method arising only at the time ofreproduction (a TE signal based on a DPD (differential phase detection)method in some cases), a reading signal of information recorded on theoptical recording medium 10, and the like. The FE signal and the TEsignal are amplified to desired levels and phase-compensated, and thenfed back to actuators 191A and 192A. These actuators 191A and 192Aperform tilt control, tracking control, focus control, and the like onthe objective lens 156A. Note that the tracking error signal generatedby the recording and reading optical system 100A is used only at thetime of reproduction.

A divergent tracking control beam 270A emitted from a light source 201Aof the tracking optical system 200A and having a red wavelength of 630to 680 nm (650 nm here) transmits through a collimating lens 253Aprovided with spherical aberration correcting means 293A, and enters apolarizing beam splitter 252A. The beam 270A having entered thepolarizing beam splitter 252A transmits through the polarizing beamsplitter 252A, and is converted to circularly polarized light as theresult of further transmitting through the quarter-wave plate 254A.Thereafter, the beam 270A is reflected by a beam splitter 260A. Thisbeam 270A is further converted to a converging beam by the objectivelens 156A, and condensed onto the servo layer 18 formed within theoptical recording medium 10. The beam 270A reflected by the servo layer18 transmits through the objective lens 156A, and is reflected by thebeam splitter 260A. The beam 270A is then converted at the quarter-waveplate 254A to linearly polarized light different by 90 degrees in phasefrom the beam 270A on an outward path. Thereafter, the beam 270A isfurther reflected by the polarizing beam splitter 252A. The beam 270Areflected by the polarizing beam splitter 252A transmits through thecondenser lens 259A, and is converted to converging light. Then, thebeam 270A goes through the cylindrical lens 257A and enters the opticaldetector 232A. Astigmatism is imparted to the beam 270A when the beamtransmits through the cylindrical lens 257A.

The optical detector 232A includes unillustrated four light-receivingunits, each of which outputs a current signal corresponding to theamount of light received. From these current signals, there is generateda tracking error (TE) signal based on a push-pull method (a trackingerror (TE) signal based on a DPD (differential phase detection) methodin some cases). Note that if information is also recorded on the servolayer 18, a reading signal may be generated from this current signal. Afocus error (FE) signal need not be generated on this optical detector232A side, but may be generated as a matter of course.

Note that as described already, the beam splitter 260A is set so as tobe large in transmittance and small in reflectance. Accordingly, part ofreturn light emitted from the light source 101A of the recording andreading optical system 100A and reflected on one of the first group ofrecording and reading layers 14 reflects on the beam splitter 260A, andadvances to the tracking optical system 200A side. Conversely, most partof return light emitted from the light source 201A of the trackingoptical system 200A and reflected on the servo layer 18 may transmitthrough the beam splitter 260A, and advance to the recording and readingoptical system 100A side. The recording and reading optical system 100Aand the tracking optical system 200A have focal positions different fromeach other within the optical recording medium 10 even in a case wherereturn light of the recording and reading optical system 100A and returnlight of the tracking optical system 200A mix with each other.Consequently, the beam 170A and the beam 270A differ in spread angle.For this reason, effects due to mixing are eliminated by extracting onlyone of the beams 170A and 270A by using a slit or an aperture having agiven shape not illustrated in particular, and then inputting the beamto the respective optical detectors 132A and 232A. As a matter ofcourse, the beams 170A and 270A may be separated from each other byusing a filter having wavelength selectivity.

If among other things, a difference between the focal position of thebeam 170A within the optical recording medium 10 in the recording andreading optical system 100A and the focal position of the beam 270Awithin the optical recording medium 10 in the tracking optical system200A is allowed to always fall within a given range, the abovementionedslit or aperture can be shaped into a simple structure. Consequently,beams can be separated from each other more simply and conveniently. Itcan be said that in order to stabilize a difference between focallengths, the focal position of the recording and reading beam 170A andthe focal position of the beam 270A for servo are preferably closer toeach other. This is because errors become smaller.

As illustrated in FIG. 21, the second optical pickup 90B is providedwith a recording and reading optical system 100B, but is not providedwith a tracking optical system. The recording and reading optical system100B serves as an optical system for performing recording/reading on asecond group of recording and reading layers 34 of the optical recordingmedium 10. Note that this recording and reading optical system 100B issubstantially the same in configuration as the recording and readingoptical system 100A of the first optical pickup 90A.

A tracking error (TE) signal obtained by irradiating the servo layer 18with light from the tracking optical system 200A of the first opticalpickup 90A is used when information is recorded on the second group ofrecording and reading layers 34 by the recording and reading opticalsystem 100B of the second optical pickup 90B. Specifically, theactuators 191B and 192B perform tilt control, tracking control, focuscontrol, and the like on the objective lens 156B by using this trackingerror signal.

Referring back to FIG. 19, the tracking control device 80 is providedwith an access controller 82, a first driver 84A, and a second driver84B. The access controller 82 controls the actuators 191A, 191B, 192Aand 192B of the first and second optical pickups 90A and 90B. Inaddition, the access controller 82 controls the first linear motionmechanism 75A and the second linear motion mechanism 75B by using thefirst driver 84A and the second driver 84B, so as to move the mechanismsto a targeted tracking position.

Specifically, the access controller 82 controls the first and secondoptical pickups 90A and 90B in the following manner.

(1) Control at the Time of Recording

The access controller 82 receives a tracking number representing arecording target from a recording and reading control device notillustrated in particular. Then, the access controller 82 applies atracking beam 270A of the first optical pickup 90A to lands/grooves ofthe servo layer 18 corresponding to this tracking number. This isrealized as the result that the access controller 82 feedback-controlsthe actuators 191A and 192A and the first linear motion mechanism 75Aupon receipt of the tracking error (TE) signal provided by the beam 270Aof the tracking optical system 200A. Under this condition, the firstoptical pickup 90A applies the recording and reading beam 170A to thefirst group of recording and reading layers 14 to record information.

At the same time, the access controller 82 controls the actuators 191Aand 192A and the second linear motion mechanism 75B by using theabovementioned tracking error (TE) signal of the first optical pickup90A. That is, the actuators 191A, 191B, 192A and 192B, the first linearmotion mechanism 75A and the second linear motion mechanism 75B takecompletely the same action in a tracking direction. Under thiscondition, the second optical pickup 90B applies the recording andreading beam 170B to the second group of recording and reading layers 34to record information. As a result, in the present embodiment, the firstand second optical pickups 90A and 90B are simultaneouslytracking-controlled, while using the common servo layer 18, tosimultaneously record information on the first and second groups ofrecording and reading layers 14 and 34.

(2) Control at the Time of Reproduction

Reproduction of the first group of recording and reading layers 14 isperformed by applying the beam 170A of the recording and reading opticalsystem 100A of the first optical pickup 90A to the first group ofrecording and reading layers 14. Tracking control at this time isrealized as the result that the access controller 82 feedback-controlsthe actuators 191A and 192A and the first linear motion mechanism 75A bydirectly using the tracking error (TE) signal of the recording andreading beam 170A, rather than using the tracking beam 270A.

Reproduction of the second group of recording and reading layers 34 isperformed by applying the beam 170B of the recording and reading opticalsystem 100B of the second optical pickup 90B to the second group ofrecording and reading layers 34. Tracking control at this time isrealized as the result that the access controller 82 feedback-controlsthe actuators 191B and 192B and the second linear motion mechanism 75Bby directly using the tracking error (TE) signal of the recording andreading beam 170B of the second optical pickup 90B. That is, in thepresent embodiment, the first and second optical pickups 90A and 90B aretracking-controlled separately from each other to simultaneouslyreproduce information recorded on the first and second groups ofrecording and reading layers 14 and 34.

The output control device 86 is provided with trial writing means 87,quality evaluating means 88, and recording power adjusting means 89.

The trial writing means 87 performs trial writing of test data on atrial writing area of each recording and reading layer of the opticalrecording medium 10 before writing actual information in a user dataarea. Specifically, first, a power setting pattern composed of simpledata which are repetitions of random data or specific data is used towrite this power setting pattern, while varying laser power stepwise.Thereafter, this power setting pattern is reproduced to select theoptimum recording power by utilizing the result of determination onsignal quality by the quality evaluating means 88. The selectedrecording power is transferred to the recording power adjusting means 89to reflect in actual output. In addition, this trial writing means 87 isprovided with memory means 87A, so as to store data on the selectedoptimum recording power in the memory means 87A.

The quality evaluating means 88 receives reproduced data on recordingmarks written on trial in the trial writing area (OPC area) of the firstor second group of recording and reading layers 14 or 34. Using thisdata, the quality evaluating means 88 detects an error rate and a SAM(Sequenced Amplitude Margin) value, and transfers the error rate and theSAM value to the trial writing means 87. Accordingly, the trial writingmeans 87 determines the quality of the reproduced data, based on whetheror not these data items satisfy given criteria, whether or not anyuncorrectable errors are present, or the like, by using the error rateand the SAM value obtained from the quality evaluating means 88. Thus,the trial writing means 87 selects recording power at which the qualityis optimum. For example, the trial writing means 87 selects the optimumrecording power at which the error rate or the SAM value is minimum.Note that the error rate and the SAM value are cited here, by way ofexample, as reference values. The present invention is not limited tothis method, but other methods may be used to determine signal quality.

In response to an instruction from the trial writing means 87, therecording power adjusting means 89 controls the recording power of thelight source 101A of the first optical pickup 90A, and the recordingpower of the light source 101B of the second optical pickup 90B.Specifically, the recording power adjusting means 89 sets recordingpower Pw, erasing power Pe, and bias power Pb in the respective lightsources 101A and 101B.

FIG. 22 illustrates an enlarged view of a cross-sectional structure ofthe optical recording medium 10 according to the present embodiment.

The optical recording medium 10 has a discoid shape, approximately 120mm in outer diameter and approximately 1.2 mm in thickness. This opticalrecording medium 10 is provided with, in order from the first surface10A side, a first cover layer 11, a first group of recording and readinglayers 14, a first group of intermediate layers 16, a first buffer layer17, a servo layer 18, a support substrate 12, a second buffer layer 37,a second group of recording and reading layers 34, a second group ofintermediate layers 36, a second cover layer 31, and a second surface30A.

The first group of recording and reading layers 14 is composed of L0 toL5 recording and reading layers 14A to 14F here, each of which has aninformation-recordable structure. These L0 to L5 recording and readinglayers 14A to 14F have a planar structure having no concavo-convexpattern and grooves for tracking control. When a high-energy beam 170 isapplied from the recording and reading optical system 100 to the L0 toL5 recording and reading layers 14A to 14F, recording marks are formedon these layers. Note that types of this first group of recording andreading layers 14 include write-once recording and reading layers onwhich information is recordable but not rewritable, and rewritablerecording and reading layers on which information is rewritable.

The support substrate 12 is a discoid-shaped substrate having athickness of 10 μm to 1200 μm, preferably within the range of 10 μm to700 μm, and more preferably within the range of 10 μm to 600 μm, orwithin the range of 100 μm to 700 μm, in order to ensure a thickness(approximately 1.2 mm) required of optical recording mediums.Specifically, in the present embodiment, the thickness of the supportsubstrate 12 is set to 500 μm and the diameter thereof is set to 120 mm.On the first surface 10A side of the support substrate 12, lands 18A andgrooves 18B are spirally formed from the vicinity of the central part ofthe support substrate 12 toward the outer edge thereof. These lands 18Aand grooves 18B serve as a concavo-convex pattern (grooves) for trackingcontrol. The concavo-convex pattern of this support substrate 12 willserve as a future servo layer 18.

The servo layer 18 formed on the support substrate 12 is composed of theconcavo-convex pattern (grooves and lands) for tracking control formedon a surface of the support substrate 12, and a reflective layerfilm-formed on the concavo-convex pattern. In the present embodiment inparticular, a metal film of Al, Ag or the like is formed as thereflective layer, so as to function as a simple light-reflecting film.This servo layer 18 is designed so as to have a transmittance of 10% orlower when a tracking beam 270A of the first optical pickup 90A isapplied to the servo layer 18. As a result, the beam 270A is preventedfrom leaking to the opposite side and turning into a noise component onthe second optical pickup 90B side. Note that in a case where arecording film which is information-recordable in addition to beingreflective is provided, the recording film may have a film configurationsubstantially the same as that of later-described recording and readinglayers 14A to 14F.

A pitch P1 between lands 18A or grooves 18B adjacent to each in theservo layer 18 is set to smaller than 0.74 μm here. Specifically, thepitch P1 is preferably set to within the range of 0.6 μm to 0.7 μm, andis more preferably set to around 0.64 μm. On the other hand, a trackpitch P2 of recording marks is set to a half (½) of the pitch P1 betweenthe lands 18A or between the grooves 18B. That is, the track pitch P2between recording marks is set to smaller than 0.37 μm, preferablywithin the range of 0.26 μm to 0.35 μm, and more preferably near 0.32μm. As a result, the track pitch P2 between recording marks is around0.32 μm compatible with the BD standard.

The pitch P1 (around 0.64 μm) between lands 18A/grooves 18B of the servolayer 18 is sized so as to enable sufficient tracking with a beam 270Ain a domain of comparatively long red wavelengths. In the presentembodiment, tracking is performed using both lands 18A and grooves 18B.As a result, the track pitch P2 of recording marks is around 0.32 μm,half the pitch P1 of the servo layer 18. As described above, trackingcontrol using both lands 18A and grooves 18B allows the track pitch P2of recording marks in the group of recording and reading layers 14 to bereduced without having to reduce the pitch P2 of the servo layer 18.

The first buffer layer 17 is formed of optically-transparent acrylicultraviolet curable resin, and is set to a film thickness of 238 μm. Forthis first buffer layer 17, there is selected a material whose amount ofabsorbed light becomes larger with a decrease in beam wavelength. Thisway of layer formation increases the amount of absorbed light of thebeam 170A having a blue wavelength and decreases the amount of absorbedlight of the beam 270A having a red wavelength. As a result, the firstbuffer layer 17 can suppress the amount of light produced when the beam170A having a blue wavelength reaches the servo layer 18 and reflects onit. Thus, signal noise at the time of reproduction can be reduced. Onthe other hand, the first buffer layer 17 allows the beam 270A having ared wavelength to actively transmit therethrough, thereby increasing theamount of light of a tracking signal.

Each layer of the first group of recording and reading layers 14 (L0 toL5 recording and reading layers 14A to 14F) stacked on the first surface10A side of the first buffer layer 17 has a three-layer structure inwhich dielectric films are stacked on both outer sides of a write-oncerecording film (not illustrated). Note that the optical reflectance,absorptance, transmittance, and the like of these L0 to L5 recording andreading layers 14A to 14F are optimized with respect to the beam 170A ina blue wavelength range (short wavelengths) of the first optical pickup90A in the recording and reading optical system 100A.

The first group of intermediate layers 16 include, in order from theside thereof farthest from the first surface 10A, L0 to L4 intermediatelayers 16A to 16E, which are stacked among the L0 to L5 recording andreading layers 14A to 14F. The respective intermediate layers 16A to 16Eare formed of acrylic or epoxy ultraviolet curable resin. The filmthicknesses of these L0 to L4 intermediate layers 16A to 16E arepreferably set to 20 μm or less, in order to increase the number oflayers. Accordingly, the L0 intermediate layer 16A is 16 μm-thick, theL1 intermediate layer 16B is 12 μm-thick, the L2 intermediate layer 16Cis 16 μm-thick, the L3 intermediate layer 16D is 12 μm-thick, and the L4intermediate layer 16E is 16 μm-thick. That is, intermediate layers oftwo types of film thicknesses (16 μm and 12 μm) are stacked in analternate manner. As a result, there are alternately set a firstdistance (16 μm) and a second distance (12 μm) different from this firstdistance, in order from the light incident surface side, as theinter-layer distances of the L0 to L5 recording and reading layers 14Ato 14F. In addition, a difference between the first distance and thesecond distance is set to 4 μm. This way of layer configuration reducesinter-layer crosstalk. As a matter of course, all layers of the firstgroup of intermediate layers 16 may be set to the same film thickness.

Like the first group of intermediate layers 16, the first cover layer 11is formed of optically-transparent acrylic ultraviolet curable resin,and is set to a film thickness of 40 μm.

The second buffer layer 37 formed on the second surface 30A side of thesupport substrate 12 is formed of optically-transparent acrylicultraviolet curable resin, and is set to a film thickness of 238 μm.

Each layer of the second group of recording and reading layers 34 (L0 toL5 recording and reading layers 34A to 34F) stacked on the secondsurface 30A side of the second buffer layer 37 has a three-layerstructure in which dielectric films are stacked on both outer sides of awrite-once recording film (not illustrated). Note that the opticalreflectance, absorptance, transmittance, and the like of these L0 to L5recording and reading layers 34A to 34F are optimized with respect tothe beam 170B in a blue wavelength range (short wavelengths) of thesecond optical pickup 90B in the recording and reading optical system100B.

The second group of intermediate layers 36 include, in order from theside thereof farthest from the second surface 30A, L0 to L4 intermediatelayers 36A to 36E, which are stacked among the L0 to L5 recording andreading layers 34A to 34F. The respective intermediate layers 36A to 36Eare formed of acrylic or epoxy ultraviolet curable resin. The filmthicknesses of these L0 to L4 intermediate layers 36A to 36E arepreferably set to 20 μm or less, in order to increase the number oflayers. Accordingly, the L0 intermediate layer 36A is 16 μm-thick, theL1 intermediate layer 36B is 12 μm-thick, the L2 intermediate layer 36Cis 16 μm-thick, the L3 intermediate layer 36D is 12 μm-thick, and the L4intermediate layer 36E is 16 μm-thick. That is, intermediate layers oftwo types of film thicknesses (16 μm and 12 μm) are stacked in analternate manner. As a result, there are alternately set a firstdistance (16 μm) and a second distance (12 μm) different from this firstdistance, in order from the second surface 30A side, as the inter-layerdistances of the L0 to L5 recording and reading layers 34A to 34F. Inaddition, a difference between the first distance and the seconddistance is set to 4 μm. This way of layer configuration reducesinter-layer crosstalk. As a matter of course, all layers of the secondgroup of intermediate layers 36 may be set to the same film thickness.

Note that the materials and the like of the second group of recordingand reading layers 34 and the second group of intermediate layers 36 arerespectively the same as those of the first group of recording andreading layers 14 and the first group of intermediate layers 16, andtherefore, will not be described again.

Like the second group of intermediate layers 36, the second cover layer31 is formed of optically-transparent acrylic ultraviolet curable resin,and is set to a film thickness of 40 μm.

As the result of the optical recording medium 10 being configured asdescribed above, an interfacial boundary (servo layer 18) between thesupport substrate 12 and the first buffer layer 17 of the opticalrecording medium 10 is positioned at a distance of 350 μm from the firstsurface 10A. In addition, the L0 recording and reading layer 14A, amongthe first group of recording and reading layers 14, farthest from thefirst surface 10A is positioned at a distance of 112 μm from the firstsurface 10A; the L1 recording and reading layer 14B is positioned at adistance of 96 μm from the first surface 10A; the L2 recording andreading layer 14C is positioned at a distance of 84 μm from the firstsurface 10A; the L3 recording and reading layer 14D is positioned at adistance of 68 μm from the first surface 10A; and the L4 recording andreading layer 14E is positioned at a distance of 56 μm from the firstsurface 10A. Yet additionally, the L5 recording and reading layer 14Fclosest to the first surface 10A is positioned at a distance of 40 μmfrom the first surface 10A. Still additionally, the overall thickness(distance between the L0 recording and reading layers 14A and the L5recording and reading layer 14F) of the first group of recording andreading layers 14 is 72 μm.

In addition, the L0 recording and reading layer 34A, among the secondgroup of recording and reading layers 34, farthest from the secondsurface 30A is positioned at a distance of 112 μm from the secondsurface 30A; the L1 recording and reading layer 34B is positioned at adistance of 96 μm from the second surface 30A; the L2 recording andreading layer 34C is positioned at a distance of 84 μm from the secondsurface 30A; the L3 recording and reading layer 34D is positioned at adistance of 68 μm from the second surface 30A; and the L4 recording andreading layer 34E is positioned at a distance of 56 μm from the secondsurface 30A. Yet additionally, the L5 recording and reading layer 34Fclosest to the second surface 30A is positioned at a distance of 40 μmfrom the second surface 30A. Still additionally, the overall thickness(distance between the L0 recording and reading layers 34A and the L5recording and reading layer 34F) of the second group of recording andreading layers 34 is 72 μm.

That is, this optical recording medium 10 has a structure symmetrized inthe thickness direction thereof, except that the servo layer 18 isarranged asymmetrically. As a result, warpage and deformation can bereduced since internal stress arises symmetrically in the thicknessdirection at the time of manufacturing the optical recording medium 10.Even if the support substrate 12 is thinned, in particular, to less than700 μm, 100 μm here, it is possible to suppress the amounts of warpageand deformation in the optical recording medium 10.

A method for producing the optical recording medium 10 according to thefifth embodiment of the present invention will next be described.

As shown in FIG. 23A, a support substrate 12 having a groove and a landformed only in its one surface is made by injection molding of apolycarbonate resin using a metallic stamper. Basic information, such asaddress information about the first recording and reading layer group 14and the second recording and reading layer group 34, recordingconditions including recording and reading powers and the positions ofor the interlayer distance between the recording and reading layers, tobe held in advance at the time of production of the medium, ispreformatted on the support substrate 12 by using a mold for injectionmolding. More specifically, the basic information is preformatted byusing wobble of the land 18A or the groove 18B. Making of the supportsubstrate 12 is not limited to injection molding. The support substrate12 may alternatively be made by a 2P method or any other method.

Thereafter, the servo layer 18 is formed on the surface of the supportsubstrate 12 in which the groove and land are provided. As the servolayer 18, film (film of a metal such as Al or Ag) reflective to thelight source in the tracking optical system 200A is formed bysputtering, for example.

Next, as shown in FIG. 23B, the first buffer layer 17 and the secondbuffer layer 37 are simultaneously formed on the two surfaces of thesupport substrate 12 on which the servo layer 18 is formed. For example,films of a viscosity-adjusted acrylic or epoxy ultraviolet curable resinare formed on the two surfaces of the support substrate 12 by spincoating or the like, and ultraviolet rays are applied to the films toform the first and second buffer layers 17 and 37.

Light-transmissive sheets formed of a light transmitting resin may beprovided in place of the ultraviolet curable resin and attached to thetwo surfaces of the support substrate 12 by using a bonding agent or anadhesive to form the first and second buffer layers 17 and 37. The firstand second buffer layers 17 and 37 may alternatively be formed byspraying, a DIP method or any other method on the two surfaces of thesupport substrate 12.

Next, as shown in FIG. 23C, the L0 recording and reading layer 14A inthe first recording and reading layer group 14 and the L0 recording andreading layer 34A in the second recording and reading layer group 34 aresimultaneously formed on the first buffer layer 17 and the second bufferlayer 37, respectively. More specifically, dielectric film, write-oncerecording film and dielectric film are formed in this order by usingvapor-phase epitaxy. It is preferable to use sputtering in particular.Thereafter, the L0 intermediate layer 16A in the first intermediatelayer group 16 is formed on the L0 recording and reading layer 14A inthe first recording and reading layer group 14, and the L0 intermediatelayer 36A in the second intermediate layer group 36 is formed on the L0recording and reading layer 34A in the second recording and readinglayer group 34. These layers are also formed simultaneously with eachother. To form the L0 intermediate layers 16A and 36A, films of aviscosity-adjusted ultraviolet curable resin, for example, are formed byspin coating or the like, and ultraviolet rays are thereafter applied tothe films so that the films are set. This procedure is repeated toalternately form the first recording and reading layer group 14 and thefirst intermediate layer group 16 on the first buffer layer 17 side andthe second recording and reading layer group 34 and the secondintermediate layer group 36 on the second buffer layer 37 side.

After the completion of forming of the L5 recording and reading layer14F in the first recording and reading layer group 14 and forming of theL5 recording and reading layer 34F in the first recording and readinglayer group 34, the first and second cover layers 11 and 31 aresimultaneously formed on these layers, as shown in FIG. 23D, therebycompleting the optical recording medium 10. To form the first and secondcover layers 11 and 31, films of a viscosity-adjusted acrylic or epoxyultraviolet curable resin, for example, are formed by spin coating orthe like, and ultraviolet rays are applied to the films so that thefilms are set. While a producing method according to the presentembodiment has been described, the present invention is not limited tothe above-described producing method. Any other producing method mayalternatively be adopted according to the present embodiment.

An optical recording and reading method for recording information on theoptical recording medium 10 and reproducing information from the opticalrecording medium 10 by using the optical recording and reading apparatus70 in the fifth embodiment of the present invention will next bedescribed. According to the optical recording and reading method in thepresent embodiment, information is simultaneously recorded in one pairof recording and reading layers consisting of one of the first recordingand reading layers 14 and one of the second recording and reading layers34 whose ordinal positions in the groups of layers from the firstsurface 10A side and from the optical recording medium 10thickness-direction-center side, respectively, coincide with each other.

The present embodiment will be described by way of example with respectto a case where information is recorded in one after another of a totalof four pairs of recording and reading layers in the first to fourthrecording patterns. In the first recording pattern, information issimultaneously recorded in the L5 recording and reading layer 14F in thefirst ordinal position from the first surface 10A side in the firstrecording and reading layers 14 and on the L0 recording and readinglayer 34A in the first ordinal position from the optical recordingmedium 10 thickness-direction-center side in the second recording andreading layers 34. In the second recording pattern, information issimultaneously recorded in the L3 recording and reading layer 14D in thethird ordinal position from the first surface 10A side in the firstrecording and reading layers 14 and on the L2 recording and readinglayer 34C in the third ordinal position from the optical recordingmedium 10 thickness-direction-center side in the second recording andreading layers 34. In the third recording pattern, information issimultaneously recorded in the L2 recording and reading layer 14C in thefourth ordinal position from the first surface 10A side in the firstrecording and reading layers 14 and on the L3 recording and readinglayer 34D in the fourth ordinal position from the optical recordingmedium 10 thickness-direction-center side in the second recording andreading layers 34.

In the fourth recording pattern, information is simultaneously recordedin the L0 recording and reading layer 14A in the sixth ordinal positionfrom the first surface 10A side in the first recording and readinglayers 14 and on the L5 recording and reading layer 34F in the sixthordinal position from the optical recording medium 10thickness-direction-center side in the second recording and readinglayers 34.

<First Recording Pattern/Simultaneous Recording in the L5 Recording andReading Layer 14F and the L0 Recording and Reading Layer 34A>

<OPC Control>

Before recording information on the optical recording medium 10, therecording power of the optical recording and reading apparatus 70 is setalong the flowchart of FIG. 24.

First, in step 300, reproducing from a DI (disc information) area in theoptical recording medium 10 is performed by the output control means 86to read basic characteristics information about the optical recordingmedium 10. In the DI area, recommended recording power P_(K) of thelaser beam is recorded as well as the kind of the medium (a write-oncetype or a rewritable type), a recording speed (1×, 2×, or the like), arecording strategy, the position of the servo layer 18, and thepositions of and the interlayer distance between the recording andreading layers. Accordingly, this recommended recording power P_(K) isset as an initial recording condition (step 302). In the presentembodiment, this DI area is formed in the servo layer 18. Accordingly,these information items are read out from the servo layer 18 by means ofthe beam 270A in the red wavelength range of the first optical pickup90A.

Next, in step 304, the output control device 86 determines, by referringto the memory means 87A, whether or not the optimum recording power ofthe first optical pickup 90A for recording in the L5 recording andreading layer 14F has already been determined by OPC. If the optimumrecording power has already been determined, the output control device86 proceeds to step 306 to apply the determined optimum recording powerto recording at the present time as well. With respect to the firstrecording pattern, the optimum recording power is undetermined.

If the optimum recording power of the first optical pickup 90A withrespect to the L5 recording and reading layer 14F is undetermined, theoutput control device 86 proceeds to step 308 to determine, by referringto the memory means 87A, whether or not the optimum recording power ofthe second optical pickup 90B for recording in the L5 recording andreading layer 34F having the same ordinal position from thethickness-direction-center side in the group of layers as that of the L5recording and reading layer 14F (i.e., the recording and reading layerat the counter position in symmetry about the center) has already beendetermined by OPC. If the optimum recording power for the L5 recordingand reading layer 34F has already been determined, the output controldevice 86 proceeds to step 310 to apply the determined optimum recordingpower as the optimum recording power of the first optical pickup 90Awith respect to the L5 recording and reading layer 14F in the firstrecording and reading layer group 14.

If the optimum recording power for the L5 recording and reading layer34F is also undetermined in step 308, the output control device 86proceeds to step 312 to record a power setting pattern (a random patternin this process) on the trial writing area X in the L5 recording andreading layer 14F (see FIG. 25A). Since the optimum recording power forthe L5 recording and reading layer 34F is also undetermined with respectto the first recording pattern, a transition to a trial writingoperation in step 312 is made.

In this case, as shown in FIG. 26, an operation to write each ofrecording powers to a power setting pattern with respect to recordingpower for actual recording is executed by making changes in a number ofsteps (P_(K+1), P_(K+2), P_(K+3), P_(K−1), P_(K−2), P_(K−3)) in twodirections to higher and lower levels with reference to the recommendedrecording power P_(K). A concrete method for recording the power settingpattern on the trial writing area X in the L5 recording and readinglayer 14F will be described in detail with respect to a first recordingand reading operation described later in detail. Therefore a descriptionof the method is omitted here.

Thereafter, in step 314, the recorded power setting pattern isreproduced by using a PRML processing device not particularlyillustrated. In step 316, the quality of the reading signal is evaluatedby the quality evaluating means 88 using the error rate or the SAM valuein the PRML processing device. The result of this evaluation istransmitted to the trial writing means 87. In step 318, the trialwriting means 87 selects the recording power at which recording isperformed with the highest quality, determines the recording power Pw ofthe light source 101A of the first optical pickup 90A, the erasing powerPe and the bias power Pb with reference to the determined power, anddesignates these powers for the recording power adjusting means 89. Bythe above-described steps, setting of the optimum recording power forthe L5 recording and reading layer 14F is completed. The optimumrecording power for the L5 recording and reading layer 14F determined bythis procedure is stored in the memory means 87A.

After determination in step 320, the process returns to theabove-described step 302 and the optimum recording power of the secondoptical pickup 90B for recording in the L0 recording and reading layer34A is set along the same procedure as that described above. Morespecifically, in step 304, the output control device 86 determines, byreferring to the memory means 87A, whether or not the optimum recordingpower of the second optical pickup 90B for recording in the L0 recordingand reading layer 34A has already been determined by OPC. If the optimumrecording power has already been determined, the output control device86 proceeds to step 306 to apply the determined optimum recording powerto recording at the present time as well. With respect to the firstrecording pattern, the optimum recording power is undetermined.

If the optimum recording power of the second optical pickup 90B withrespect to the L0 recording and reading layer 34A is undetermined, theoutput control device 86 proceeds to step 308 to determine, by referringto the memory means 87A, whether or not the optimum recording power ofthe first optical pickup 90A for recording in the L0 recording andreading layer 14A having the same ordinal position from thethickness-direction-center side in the group of layers as that of the L0recording and reading layer 34A has already been determined by OPC. Ifthe optimum recording power for the L0 recording and reading layer 14Ahas already been determined, the output control device 86 proceeds tostep 310 to apply the determined optimum recording power as the optimumrecording power of the second optical pickup 90B with respect to the L0recording and reading layer 34A in the second recording and readinglayer group 34.

If the optimum recording power of the first optical pickup 90A forrecording in the L0 recording and reading layer 14A is also undeterminedin step 308, the output control device 86 proceeds to step 312 to recordthe power setting pattern (a random pattern in this process) on thetrial writing area X in the L0 recording and reading layer 34A. Sincethe optimum recording power of the first optical pickup 90A forrecording in the L0 recording and reading layer 14A is also undeterminedwith respect to the first recording pattern, a transition to the trialwriting operation in step 312 is made (see FIG. 25A).

Thereafter, in step 314, the recorded power setting pattern isreproduced by using the PRML processing device not particularlyillustrated. In step 316, the quality of the reading signal is evaluatedby the quality evaluating means 88. In step 318, the optimum recordingpower of the light source 101B of the second optical pickup 90B withrespect to the L0 recording and reading layer 34A is determined. Theoptimum recording power for the L0 recording and reading layer 34Adetermined by the above-described steps is stored in the memory means87A.

<Simultaneous Recording of Information in the L5 Recording and ReadingLayer 14F and the L0 Recording and Reading Layer 34A>

As already described, in the present embodiment, information issimultaneously recorded in one pair of recording and reading layersconsisting of one of the first recording and reading layers 14 and oneof the second recording and reading layers 34 whose ordinal positions inthe groups of layers from the first surface 10A side and from theoptical recording medium 10 thickness-direction-center side,respectively, coincide with each other. More specifically, as a firstrecording and reading operation, for recording information in the L5recording and reading layer 14F in the first recording and reading layergroup 14, tracking is first performed by applying to the servo layer 18the beam 270A in the red wavelength range from the tracking opticalsystem 200A of the first optical pickup 90A. To be more specific,tracking is performed by applying a spot of the beam 270A to the groove18B and the land 18A in the servo layer 18. Simultaneously withtracking, the recording beam 170A in the blue wavelength range from therecording and reading optical system 100A of the first optical pickup90A is applied to the L5 recording and reading layer 14F.

Thus, while the groove 18B and the land 18A are being tracked,information is recorded in the L5 recording and reading layer 14F alongthe groove 18B and the land 18A. As a result, the track pitch P2 betweenthe recording marks formed in the L5 recording and reading layer 14F ishalf the pitch P1 between the grooves 18B.

As a second recording and reading operation, at the time of recording ofinformation in the L0 recording and reading layer 34A in the secondrecording and reading layer group 34, tracking control of the secondoptical pickup 90B is performed by using the tracking error signal fromthe tracking optical system 200A of the first optical pickup 90A. As aresult, the first optical pickup 90A and the second optical pickup 90Balways exist at the same position with respect to the trackingdirection. Simultaneously with tracking, the recording beam 170B in theblue wavelength range from the recording and reading optical system 100Bof the second optical pickup 90B is applied to the L0 recording andreading layer 34A. As a result, information is recorded in the L0recording and reading layer 34A. The track pitch P2 between therecording marks formed in the L0 recording and reading layer 34A is alsoa half of the pitch P1 between the grooves of the servo layer 18.

The above-described first and second recording and reading operationsare concurrently advanced to realize simultaneous recording ofinformation in the first and second recording and reading layer groups14 and 34. The recording power Pw, the erasing power Pe and the biaspower Pb at the time of performing this simultaneous recording are setby the above-described OPC operation.

After the completion of necessary information in the L0 recording andreading layer 14A in the first recording and reading layer group 14 andthe L0 recording and reading layer 34A in the second recording andreading layer group 34, additional information to be recorded at thepresent time (e.g., address information about recording and contentinformation) is simultaneously recorded in management areas secured inadvance in portions of the L0 recording and reading layers 14A and 34A.

<Second Recording Pattern/Simultaneous Recording in the L3 Recording andReading Layer 14D and the L2 Recording and Reading Layer 34C>

<OPC Control>

The recording power of the optical recording and reading apparatus 70 isset along the flowchart of FIG. 24.

First, in step 300, reproducing from the DI (disc information) area inthe optical recording medium 10 is performed by the output control means86 to read the basic characteristics information about the opticalrecording medium 10, and the recommended recording power P_(K) in thisinformation is set as an initial recording condition (step 302).

Next, in step 304, the output control device 86 determines, by referringto the memory means 87A, whether or not the optimum recording power ofthe first optical pickup 90A for recording in the L3 recording andreading layer 14D has already been determined by OPC. If the optimumrecording power has already been determined, the output control device86 proceeds to step 306 to apply the determined optimum recording powerto recording at the present time as well. With respect to the secondrecording pattern, the optimum recording power is undetermined.

If the optimum recording power of the first optical pickup 90A withrespect to the L3 recording and reading layer 14D is undetermined, theoutput control device 86 proceeds to step 308 to determine, by referringto the memory means 87A, whether or not the optimum recording power ofthe second optical pickup 90B for recording in the L3 recording andreading layer 34D having the same ordinal position from thethickness-direction-center side in the group of layers as that of the L3recording and reading layer 14D (i.e., the recording and reading layerat the counter position in symmetry about the center) has already beendetermined by OPC. If the optimum recording power for the L3 recordingand reading layer 34D has already been determined, the output controldevice 86 proceeds to step 310 to apply the determined optimum recordingpower as the optimum recording power of the first optical pickup 90Awith respect to the L3 recording and reading layer 14D in the firstrecording and reading layer group 14.

If the optimum recording power for the L3 recording and reading layer34D is also undetermined in step 308, the output control device 86proceeds to step 312 to record a power setting pattern (a random patternin this process) on the trial writing area X in the L3 recording andreading layer 14D (see FIG. 25A). Since the optimum recording power forthe L3 recording and reading layer 34D is also undetermined with respectto the second recording pattern, a transition to a trial writingoperation in step 312 is made.

Thereafter, in step 314, the recorded power setting pattern isreproduced. In step 316, the quality of the reading signal is evaluatedby the quality evaluating means 88. In step 318, the trial writing means87 determines the optimum recording power of the first optical pickup90A. The optimum recording power for the L3 recording and reading layer14D determined by this procedure is stored in the memory means 87A.

Next, the process returns to the above-described step 302 and theoptimum recording power of the second optical pickup 90B for recordingin the L2 recording and reading layer 34C is set along the sameprocedure as that described above. More specifically, in step 304, theoutput control device 86 determines, by referring to the memory means87A, whether or not the optimum recording power of the second opticalpickup 90B for recording in the L2 recording and reading layer 34C hasalready been determined by OPC. If the optimum recording power hasalready been determined, the output control device 86 proceeds to step306 to apply the determined optimum recording power to recording at thepresent time as well. With respect to the second recording pattern, theoptimum recording power is undetermined.

If the optimum recording power of the second optical pickup 90B withrespect to the L2 recording and reading layer 34C is undetermined, theoutput control device 86 proceeds to step 308 to determine, by referringto the memory means 87A, whether or not the optimum recording power ofthe first optical pickup 90A for recording in the L2 recording andreading layer 14C having the same ordinal position from the thicknessdirection center side in the group of layers as that of the L2 recordingand reading layer 34C has already been determined by OPC. If the optimumrecording power for the L2 recording and reading layer 14C has alreadybeen determined, the output control device 86 proceeds to step 310 toapply the determined optimum recording power as the optimum recordingpower of the second optical pickup 90B with respect to the L2 recordingand reading layer 34C in the second recording and reading layer group34.

If the optimum recording power for recording in the L2 recording andreading layer 14C is also undetermined in step 308, the output controldevice 86 proceeds to step 312 to record a power setting pattern (arandom pattern in this process) on the trial writing area X in the L2recording and reading layer 34C. Since the optimum recording power forrecording in the L2 recording and reading layer 14C is also undeterminedwith respect to the second recording pattern, a transition to the trialwriting operation in step 312 is made (see FIG. 25B).

Thereafter, in step 314, the recorded power setting pattern isreproduced by using the PRML processing device not particularlyillustrated. In step 316, the quality of the reading signal is evaluatedby the quality evaluating means 88. In step 318, the optimum recordingpower of the light source 101B of the second optical pickup 90B withrespect to the L2 recording and reading layer 34C is determined. Theoptimum recording power for the L2 recording and reading layer 34Cdetermined by the above-described steps is stored in the memory means87A.

<Simultaneous Recording of Information in the L3 Recording and ReadingLayer 14D and the L2 Recording and Reading Layer 34C>

An operation to record information is performed as a first recording andreading operation by applying to the L3 recording and reading layer 14Dthe recording beam 170A in the blue wavelength range from the recordingand reading optical system 100A of the first optical pickup 90A whileperforming tracking by applying to the servo layer 18 the beam 270A inthe red wavelength range from the tracking optical system 200A of thefirst optical pickup 90A.

An operation to record information is performed as a second recordingand reading operation by applying to the L2 recording and reading layer34C the recording beam 170B in the blue wavelength range from therecording and reading optical system 100B of the second optical pickup90B while performing tracking control of the second optical pickup 90Bby using the tracking error signal from the tracking optical system 200Aof the first optical pickup 90A.

The above-described first and second recording and reading operationsare concurrently advanced to realize simultaneous recording ofinformation in the first and second recording and reading layer groups14 and 34 (see FIG. 27B). The recording power Pw, the erasing power Peand the bias power Pb at the time of performing this simultaneousrecording are set by the above-described OPC operation.

<Third Recording Pattern/Simultaneous Recording in the L2 Recording andReading Layer 14C and the L3 Recording and Reading Layer 34D>

<OPC Control>

The recording power of the optical recording and reading apparatus 70 isset along the flowchart of FIG. 24.

First, in step 300, reproducing from the DI (disc information) area inthe optical recording medium 10 is performed by the output control means86 to read the basic characteristics information about the opticalrecording medium 10, and the recommended recording power P_(K) in thisinformation is set as an initial recording condition (step 302).

Next, in step 304, the output control device 86 determines, by referringto the memory means 87A, whether or not the optimum recording power ofthe first optical pickup 90A for recording in the L2 recording andreading layer 14C has already been determined by OPC. If the optimumrecording power has already been determined, the output control device86 proceeds to step 306 to apply the determined optimum recording powerto recording at the present time as well. With respect to the thirdrecording pattern, the optimum recording power is undetermined.

If the optimum recording power of the first optical pickup 90A withrespect to the L2 recording and reading layer 14C is undetermined, theoutput control device 86 proceeds to step 308 to determine, by referringto the memory means 87A, whether or not the optimum recording power ofthe second optical pickup 90B for recording in the L2 recording andreading layer 34C having the same ordinal position from the thicknessdirection center side in the group of layers as that of the L2 recordingand reading layer 14C (i.e., the recording and reading layer at thecounter position in symmetry about the center) has already beendetermined by OPC. If the optimum recording power for the L2 recordingand reading layer 34C has already been determined, the output controldevice 86 proceeds to step 310 to apply the determined optimum recordingpower as the optimum recording power of the first optical pickup 90Awith respect to the L2 recording and reading layer 14C in the firstrecording and reading layer group 14.

In the present embodiment, the optimum recording power of the secondoptical pickup 90B for recording in the L2 recording and reading layer34C is already stored in the memory means 87A in the second recordingpattern. In step 310, therefore, this optimum recording power can beused as the optimum recording power of the first optical pickup 90A withrespect to the L2 recording and reading layer 14C. As a result, thetrial writing operation from step 312 to step 318 is omitted (see FIG.25C).

The optimum recording power for the L2 recording and reading layer 14Cdetermined by the above-described steps is stored in the memory means87A.

Next, the process returns to step 302 and the optimum recording power ofthe second optical pickup 90B for recording in the L3 recording andreading layer 34D is set along the same procedure as that describedabove. More specifically, in step 304, the output control device 86determines, by referring to the memory means 87A, whether or not theoptimum recording power of the second optical pickup 90B for recordingin the L3 recording and reading layer 34D has already been determined byOPC. If the optimum recording power has already been determined, theoutput control device 86 proceeds to step 306 to apply the determinedoptimum recording power to recording at the present time as well. Withrespect to the third recording pattern, the optimum recording power isundetermined.

If the optimum recording power of the second optical pickup 90B withrespect to the L3 recording and reading layer 34D is undetermined, theoutput control device 86 proceeds to step 308 to determine, by referringto the memory means 87A, whether or not the optimum recording power ofthe first optical pickup 90A for recording in the L3 recording andreading layer 14D having the same ordinal position from thethickness-direction-center side in the group of layers as that of the L3recording and reading layer 34D has already been determined by OPC. Ifthe optimum recording power for the L3 recording and reading layer 14Dhas already been determined, the output control device 86 proceeds tostep 310 to apply the determined optimum recording power as the optimumrecording power of the second optical pickup 90B with respect to the L3recording and reading layer 34D in the second recording and readinglayer group 34.

In the present embodiment, the optimum recording power of the firstoptical pickup 90A for recording in the L3 recording and reading layer14D is already stored in the memory means 87A in the second recordingpattern. In step 310, therefore, this optimum recording power can beused as the optimum recording power of the second optical pickup 90Bwith respect to the L3 recording and reading layer 34D. As a result, thetrial writing operation from step 312 to step 318 is omitted (see FIG.25C).

The optimum recording power for the L3 recording and reading layer 34Ddetermined by the above-described steps is stored in the memory means87A.

<Simultaneous Recording of Information in the L2 Recording and ReadingLayer 14C and the L3 Recording and Reading Layer 34D>

An operation to record information is performed as a first recording andreading operation by applying to the L2 recording and reading layer 14Cthe recording beam 170A in the blue wavelength range from the recordingand reading optical system 100A of the first optical pickup 90A whileperforming tracking by applying to the servo layer 18 the beam 270A inthe red wavelength range from the tracking optical system 200A of thefirst optical pickup 90A.

An operation to record information is performed as a second recordingand reading operation by applying to the L3 recording and reading layer34D the recording beam 170B in the blue wavelength range from therecording and reading optical system 100B of the second optical pickup90B while performing tracking control of the second optical pickup 90Bby using the tracking error signal from the tracking optical system 200Aof the first optical pickup 90A.

The above-described first and second recording and reading operationsare concurrently advanced to realize simultaneous recording ofinformation in the first and second recording and reading layer groups14 and 34 (see FIG. 27C). The recording power Pw, the erasing power Peand the bias power Pb at the time of performing this simultaneousrecording are set by the above-described OPC operation.

<Fourth Recording Pattern/Simultaneous Recording in the L0 Recording andReading Layer 14A and the L5 Recording and Reading Layer 34F>

<OPC Control>

The recording power of the optical recording and reading apparatus 70 isset along the flowchart of FIG. 24.

First, in step 300, reproducing from the DI (disc information) area inthe optical recording medium 10 is performed by the output control means86 to read the basic characteristics information about the opticalrecording medium 10, and the recommended recording power P_(K) in thisinformation is set as an initial recording condition (step 302).

Next, in step 304, the output control device 86 determines, by referringto the memory means 87A, whether or not the optimum recording power ofthe first optical pickup 90A for recording in the L0 recording andreading layer 14A has already been determined by OPC. If the optimumrecording power has already been determined, the output control device86 proceeds to step 306 to apply the determined optimum recording powerto recording at the present time as well. With respect to the fourthrecording pattern, the optimum recording power is undetermined.

If the optimum recording power of the first optical pickup 90A withrespect to the L0 recording and reading layer 14A is undetermined, theoutput control device 86 proceeds to step 308 to determine, by referringto the memory means 87A, whether or not the optimum recording power ofthe second optical pickup 90B for recording in the L0 recording andreading layer 34A having the same ordinal position from thethickness-direction-center side in the group of layers as that of the L0recording and reading layer 14A (i.e., the recording and reading layerat the counter position in symmetry about the center) has already beendetermined by OPC. If the optimum recording power for the L0 recordingand reading layer 34A has already been determined, the output controldevice 86 proceeds to step 310 to apply the determined optimum recordingpower as the optimum recording power of the first optical pickup 90Awith respect to the L0 recording and reading layer 14A in the firstrecording and reading layer group 14.

In the present embodiment, the optimum recording power of the secondoptical pickup 90B for recording in the L0 recording and reading layer34A is already stored in the memory means 87A in the first recordingpattern. In step 310, therefore, this optimum recording power can beused as the optimum recording power of the first optical pickup 90A withrespect to the L0 recording and reading layer 14A. As a result, thetrial writing operation from step 312 to step 318 is omitted (see FIG.25D).

The optimum recording power for the L0 recording and reading layer 14Adetermined by the above-described steps is stored in the memory means87A.

Next, the process returns to step 302 and the optimum recording power ofthe second optical pickup 90B for recording in the L5 recording andreading layer 34F is set along the same procedure as that describedabove. More specifically, in step 304, the output control device 86determines, by referring to the memory means 87A, whether or not theoptimum recording power of the second optical pickup 90B for recordingin the L5 recording and reading layer 34F has already been determined byOPC. If the optimum recording power has already been determined, theoutput control device 86 proceeds to step 306 to apply the determinedoptimum recording power to recording at the present time as well. Withrespect to the fourth recording pattern, the optimum recording power isundetermined.

If the optimum recording power of the second optical pickup 90B withrespect to the L5 recording and reading layer 34F is undetermined, theoutput control device 86 proceeds to step 308 to determine, by referringto the memory means 87A, whether or not the optimum recording power ofthe first optical pickup 90A for recording in the L5 recording andreading layer 14F having the same ordinal position from thethickness-direction-center side in the group of layers as that of the L5recording and reading layer 34F has already been determined by OPC. Ifthe optimum recording power for the L5 recording and reading layer 14Fhas already been determined, the output control device 86 proceeds tostep 310 to apply the determined optimum recording power as the optimumrecording power of the second optical pickup 90B with respect to the L5recording and reading layer 34F in the second recording and readinglayer group 34.

In the present embodiment, the optimum recording power of the firstoptical pickup 90A for recording in the L5 recording and reading layer14F is already stored in the memory means 87A in the first recordingpattern. In step 310, therefore, this optimum recording power can beused as the optimum recording power of the second optical pickup 90Bwith respect to the L5 recording and reading layer 34F. As a result, thetrial writing operation from step 312 to step 318 is omitted (see FIG.25D).

The optimum recording power for the L5 recording and reading layer 34Fdetermined by the above-described steps is stored in the memory means87A.

<Simultaneous Recording of Information in the L0 Recording and ReadingLayer 14A and the L5 Recording and Reading Layer 34F>

An operation to record information is performed as a first recording andreading operation by applying to the L0 recording and reading layer 14Athe recording beam 170A in the blue wavelength range from the recordingand reading optical system 100A of the first optical pickup 90A whileperforming tracking by applying to the servo layer 18 the beam 270A inthe red wavelength range from the tracking optical system 200A of thefirst optical pickup 90A.

An operation to record information is performed as a second recordingand reading operation by applying to the L5 recording and reading layer34F the recording beam 170B in the blue wavelength range from therecording and reading optical system 100B of the second optical pickup90B while performing tracking control of the second optical pickup 90Bby using the tracking error signal from the tracking optical system 200Aof the first optical pickup 90A.

The above-described first and second recording and reading operationsare concurrently advanced to realize simultaneous recording ofinformation in the first and second recording and reading layer groups14 and 34 (see FIG. 27D). The recording power Pw, the erasing power Peand the bias power Pb at the time of performing this simultaneousrecording are set by the above-described OPC operation.

While a case where management areas are secured in the L0 recording andreading layers 14A and 34A has been described by way of example, theother recording and reading layers area also available. In a case wherethe servo layer 18 has a recording film, it is preferable that amanagement area be secured in the servo layer 18, and that additionalinformation be recorded in the management area. For this recording, thebeam 270A, with which tracking control is performed, may be used.Gathering management information in the servo layer 18 enablessimultaneously grasping the management information about the firstrecording and reading layer group 14 and the second recording andreading layer group 34.

A case where OPC control is performed each time one pair of recordingand reading layers are selected in the process from the first recordingpattern to the fourth recording pattern has been described by way ofexample. However, the present invention is not limited to this. Forexample, the optimum recording powers for the four pairs of recordingand reading layers as recording/reading targets may be determined andstored in the memory means 87A by executing in advance the OPC controldescribed with respect to the first to fourth recording patterns, andonly the recording operation described with respect to the first tofourth recording patterns may thereafter be continuously performed. Thisprocedure is also preferable. Processing in this way enables maintainingthe continuity of the transfer rate at the time of recording informationover a plurality of recording and reading layers.

<Simultaneous Reproducing of Information from First and Second Recordingand Reading Layer Groups>

In the present embodiment, information simultaneously recorded in thefirst and second recording and reading layer groups 14 and 34 issimultaneously reproduced. For example, as shown in FIG. 28, when theinformation in the L5 recording and reading layer 14F in the firstrecording and reading layer group 14 is reproduced, a first reproducingoperation is performed by applying to the L5 recording and reading layer14F the beam 170A from the recording and reading optical system 100A ofthe first optical pickup 90A and by performing tracking control andfocus control.

Also, when the information in the L0 recording and reading layer 34A inthe second recording and reading layer group 34 is reproduced, a secondreproducing operation is performed by applying to the L0 recording andreading layer 34A the beam 170B from the recording and reading opticalsystem 100B of the second optical pickup 90B and by performing trackingcontrol and focus control. These first and second recording and readingoperations are concurrently advanced to realize simultaneous reproducingof information from the first and second recording and reading layergroups 14 and 34. While tracking control is performed by using the servolayer 18 at the time of recording, the first and second optical pickups90A and 90B are respectively controlled independently in tracking byusing the respective recording and reading optical systems 100A and100B.

According to the optical recording and reading method in the fifthembodiment, the first recording and reading operation using the firstoptical pickup 90A and the second recording and reading operation usingthe second optical pickup 90B are simultaneously executed tosimultaneously record information in the first and second recording andreading layer groups 14 and 34 or simultaneously reproduce informationfrom the first and second recording and reading layer groups 14 and 34.As a result, a leap upward in transfer rate at the time or recording orreading is realized.

In the present embodiment in particular, information is simultaneouslyrecorded in one pair of recording and reading layers consisting of oneof the first recording and reading layers 14 and one of the secondrecording and reading layers 34 whose ordinal positions in the groups oflayers from the first surface 10A side and from the optical recordingmedium 10 thickness-direction-center side, respectively, coincide witheach other. This may be generalized to conceive selecting one pair ofrecording and reading layers on which simultaneous recording is to beperformed such that if each of the numbers of layers in the first andsecond recording and reading layer groups 14 and 34 is set to S (S: anatural number equal to or larger than 2), the sum (X+Y) of the ordinalposition from the thickness-direction center of the recording andreading layer as a recording target in the first recording and readinglayer group 14 (the X-th position in this description) and the ordinalposition from the thickness-direction center of the recording andreading layer as a recording target in the second recording and readinglayer group 34 (the Y-th position in this description) is invariably(S+1). For example, in the present embodiment, selection may be made sothat the sum of the ordinal position from the thickness-direction centerof the recording and reading layer as a recording target in the firstrecording and reading layer group 14 (e.g., the second position: theposition of the L1 recording and reading layer 14B) and the ordinalposition from the thickness-direction center of the recording andreading layer as a recording target in the second recording and readinglayer group 34 (e.g., the fifth position: the position of the L4recording and reading layer 34E) is invariably 7.

In this way, the interfocal distance T (see FIG. 27) between the focalpoint of the recording and reading beam 170A on the first optical pickup90A side and the focal point of the recording and reading beam 170B onthe second optical pickup 90B side can be made constant or comparativelystable. More specifically, in the present embodiment, the focal point ofthe beam 170A is moved from the first surface 10A side toward the centerside, as indicated by arrows Q in FIG. 27, while the focal point of thebeam 170B is moved from the center side to the second surface 30A side,as indicated by arrows Q in FIG. 27. As a result, the interfocaldistance T between the pair of beams 170A and 170B is always constantand the number of intermediate layers 16 and 36 existing between thefocal points is also constant. Thus, limiting the amount of change ininterfocal distance T due to errors in film forming of the intermediatelayer groups 16 and 36 within a certain range is enabled. Thiscontributes to reducing focus errors or the like. In particular, evenwhen the beams 170A and 170B jump to the next recording and readinglayers, the probability of jumping to a wrong one of the recording andreading layers can be reduced if the focal points of the beams 170A and170B are simultaneously moved while the interfocal distance T is fixed.

The present embodiment has been described with respect to a case whererecording on the first recording and reading layer group 14 progressesfrom the first surface 10A side toward the center side and recording onthe second recording and reading layer group 34 progresses from thecenter side toward the second surface 30A side. However, the presentinvention is not limited to this. Recording may be performed by randomlyselecting from the pairs of recording and reading layers may be randomlymade as long as recording is performed on each pair of recording andreading layers consisting of one of the first recording and readinglayers 14 and one of the second recording and reading layers 34 whoseordinal positions in the groups of layers from the first surface 10Aside and from the optical recording medium 10 thickness-direction-centerside, respectively, coincide with each other.

Further, in the present embodiment, the operation to record information,as the first recording and reading operation, is performed by applyingthe recording and reading beam 170A from the first optical pickup 90A tothe first recording and reading layer group 14 while performing trackingcontrol by applying the tracking beam 270A to the servo layer 18. On theother hand, in the second recording and reading operation, the secondoptical pickup 90B is controlled in tracking with respect to the secondrecording and reading layer group 34 by using the beam 270A and theservo layer 18 used in the first recording and reading operation, andthe recording and reading beam 170B from the second optical pickup 90Bis applied to record information. Therefore, the second optical pickup90B in the optical recording and reading apparatus 70 can be providedwithout a tracking optical system, thus enabling simplification of thestructure.

In the OPC control in the present embodiment, as described withreference to the flowchart of FIG. 24, if the optimum recording power ofthe recording and reading beam 170A for recording in the recording andreading layer in the n-th position from the optical recording medium 10thickness-direction-center side in the first recording and reading layergroup 14 is undetermined, determination is made by referring to thememory means 87A as to whether or not the optimum recording power of therecording and reading beam 107B for recording in the recording andreading layer in the n-th position from the center side in the secondrecording and reading layer group 34 has already been determined by OPCcontrol and, if this optimum recording power has already beendetermined, this optimum recording power is determined as the optimumrecording power of the first recording and reading beam 170A. Only ifthe optimum recording power of the recording and reading beam 170B withrespect to the second recording and reading layer group 34 isundetermined, trial writing to the trial writing area in the n-threcording and reading layer in the first recording and reading layergroup 14 is performed with the recording and reading beam 170A todetermine the optimum recording power of the recording and reading beam170A.

Similarly, if the optimum recording power of the recording and readingbeam 170B for recording in the recording and reading layer in the m-thposition from the optical recording medium 10 thickness-direction-centerside in the second recording and reading layer group 34 is undetermined,determination is made by referring to the memory means 87A as to whetheror not the optimum recording power of the recording and reading beam107A for recording in the recording and reading layer in the m-thposition from the center side in the first recording and reading layergroup 14 has already been determined by OPC control and, if this optimumrecording power has already been determined, this optimum recordingpower is determined as the optimum recording power of the secondrecording and reading beam 170B. Only if the optimum recording power ofthe recording and reading beam 170A with respect to the first recordingand reading layer group 14 is undetermined, trial writing to the trialwriting area in the m-th recording and reading layer in the secondrecording and reading layer group 34 is performed with the recording andreading beam 170B to determine the optimum recording power of therecording and reading beam 170B.

In the optical recording medium 10, the pair of recording and readinglayers having the same ordinal positions from the thickness-directioncenter (the n-th position, the m-th position) in the groups of layershave recording characteristics approximate to each other because theirdistances from the first and second surfaces 10A and 30A and the beampaths thereto are in a symmetrical relationship with each other.Therefore, if the optimum recording power for one of the pair ofrecording and reading layers having the same ordinal positions from thethickness-direction center (the n-th position, the m-th position) in thegroups of layers is already determined when the optimum recording powerswith respect to the recording and reading layers in the first and secondrecording and reading layer groups 14 and 34 are individually set, thedetermined optimum recording power is used as the optimum recordingpower for the other recording and reading layer. The need for the trialwriting is correspondingly reduced, thus largely reducing the OPC time.

As shown in FIG. 25 in particular, with the progress of recording fromthe first recording pattern to the fourth recording pattern, the numberof kinds of optimum recording power stored in the memory means 87A isincreased and, therefore, the need to perform trial writing to the trialwriting area X for OPC is reduced, thereby further reducing the OPCtime.

Thus, OPC control in the present embodiment is capable of reducing thetrial writing area X needed in the first and second recording andreading layer groups 14 and 34 to a half. Accordingly, the size of thetrial writing area X can be reduced in comparison with the case wherethe trial writing areas X are formed in all the recording and readinglayers. This effect contributes to an increase in user data area in thefirst and second recording and reading layer groups 14 and 34.

Further, according to this optical recording and reading method,information can be recorded in the first and second recording andreading layer groups 14 and 34 by using the two independent recordingand reading beams 170A and 170B. Therefore, the ranges of movement ofthe focal points of the recording and reading beams 170A and 170B fromthe first and second optical pickups 90A and 90B can be separately setin the thickness direction. As a result, a state advantageous against acomatic aberration under a tilt condition, for example, can beestablished even when the number of recording and reading layers isincreased.

Specifically, according to the optical recording and reading method, therecording and reading beam 170A from the first optical pickup 90A usedin the first recording and reading operation is caused to enter theoptical recording medium 10 through the first surface 10A of the same,while the recording and reading beam 170B from the second optical pickup90B used in the second recording and reading operation is caused toenter the optical recording medium 10 through the second surface 30A ofthe same. For example, recording is performed on the first recording andreading layers 14 disposed on one side with respect to the center in thethickness direction of the optical recording medium 10 with the firstoptical pickup 90A for performing the first recording and readingoperation, while recording is performed on the second recording andreading layers 34 disposed on the other side with respect to the centerin the thickness direction of the optical recording medium 10 with thesecond optical pickup 90B for performing the second recording andreading operation. As a result, as in the optical recording medium 10,the first recording and reading layers 14 can be brought closer to thefirst surface 10A and the second recording and reading layers 34 can bebrought closer to the second surface 30A. Therefore, this recording andreading method is advantageous against a comatic aberration under a tiltcondition, for example, while the number of recording and reading layersis increased.

In the optical recording medium 10 used in the present embodiment, thefirst recording and reading layer group 14 and the second recording andreading layer group 34 are disposed in such positions as to be in asymmetrical relationship with each other with respect to the center inthe thickness direction of the optical recording medium 10. Therefore,optical designing of the first and second optical pickups 90A and 90B,recognition of the positions of the recording and reading layers, focuscontrol, etc. of the optical recording and reading apparatus 70, can beperformed in common ways, so that an increase in recording and readingspeed can be achieved. Also, in the optical recording medium 10,internal stresses produced in the first and second recording and readinglayer groups 14 and 34 are also in a symmetrical relationship in thethickness direction. This contributes to limiting of warpage of theoptical recording medium 10. Even in the L5 recording and reading layers14F and 34F remotest from the servo layer 18, therefore, deviations inthe radial direction cannot be easily caused in forming of recordingmarks. As a result, in the trial writing area X, an error range to beconsidered in advance can be set smaller.

Further, according to this optical recording and reading method, therecording and reading beam 170A from the first optical pickup 90A andthe recording and reading beam 170B from the second optical pickup 90Bare placed at different positions in the circumferential direction onthe optical recording medium 10. Even if lights in the beams 170A and170B pass through the surfaces at the opposite sides, a bad influence ofthe leakage light on the reproduced waveforms can be avoided. If a largeamount of light in the tracking beam 270 applied to the servo layer 18passes through the servo layer 18, a bad influence can be easilyproduced on the second optical pickup 90B side. In the optical recordingmedium 10, therefore, the transmittance of the servo layer 18 to thebeam 270A may be set to 10% or less to limit the bad influence of thebeam 270A on the second optical pickup 90B side.

In the optical recording medium 10 to which the optical recording andreading method in the present embodiment is applied, the servo layer 18is formed only on one surface of the support substrate 12, and the firstrecording and reading layer group 14 and the second recording andreading layer group 34 are disposed on the two surfaces of the supportsubstrate 12. Therefore, the internal stresses caused when the first andsecond recording and reading layer groups 14 and 34 are formed aredispersed on the opposite sides of the support substrate 12. As aresult, warpage and deformation of the optical recording medium 10 canbe limited. Dispersing internal stresses in this way enables limiting ofwarpage of the optical recording medium 10 even when the thickness ofthe support substrate 12 is set within the range from 100 to 1000 μm.

An attempt to form a concavo-convex pattern for tracking on the oppositesides of the support substrate 12 entails complicating the process offorming the support substrate 12 and increasing the probability of theaccuracy of the support substrate 12 being reduced. In the presentembodiment, therefore, a concavo-convex pattern for tracking are formedon one side of the support substrate 12 and the production of thesupport substrate 12 is simplified, thereby improving the accuracy. Evenif such a construction using a single servo layer 18 is adopted,sufficiently high accuracy of recording with the optical recording andreading apparatus 70 can be maintained because tracking control of thefirst and second optical pickups 90A and 90B disposed on the oppositesides is performed by using one beam 270A.

Further, in the optical recording medium 10, the thicknesses of thefirst buffer layer 17 and the second buffer layer 37 are setsubstantially equal to each other. As a result, warpage of the supportsubstrate 12 in the process of forming the first and second bufferlayers 17 and 37 can be limited. This means that the support substrate12 can be reduced in thickness or formed of a material of lowerrigidity. The space in the thickness direction in which recording andreading layers are formed can be increased by an amount corresponding tothe reduction in thickness of the support substrate 12.

In the present embodiment in particular, the first buffer layer 17 andthe second buffer layer 37, the first recording and reading layer group14 and the second recording and reading layer group 34, and the firstintermediate layer group 16 and the second intermediate layer group 36are simultaneously formed on the opposite surfaces when the opticalrecording medium 10 is made. As a result, internal stresses caused atthe time of ultraviolet curing act uniformly on the opposite sides ofthe support substrate 12, so that warpage of the optical recordingmedium 10 can be further reduced.

Further, in the optical recording medium 10, the reflectance of theservo layer 18 when the beam 270A with red wavelengths for tracking isapplied is set higher than that when the recording and reading beam 170Ais experimentally applied to the servo layer 18. More specifically, torealize this, a material that absorbs a larger amount of light if thewavelength of the beam is shorter is selected with respect to the firstbuffer layer 17. In this way, the amount of light reaching the servolayer 18 (the amount of reflected light from the servo layer 18) can belimited, because even when light in the recording and reading beam 170Ain the blue wavelength range is incident on the servo layer 18, it canbe easily absorbed by the first buffer layer 17. On the other hand, thetracking beam 270A from the first optical pickup 90A can positively passthrough the first buffer layer 17. Therefore the amount of lightreaching the servo layer 18 (the amount of reflected light from theservo layer 18) can be increased. As a result, the quality of thereading signal can be improved and stable tracking control can berealized.

In the present embodiment, characteristics of different opticalabsorptivities to a red wavelength and a blue wavelength are imparted inthe first buffer layer 17, so that the servo layer 18 has differentreflectances to the tracking beam and the recording and reading beam.However, the present invention is not limited to this. For example,reflecting film itself, formed in the servo layer 18, may be givenwavelength selectivity such as to have different reflectances withrespect to wavelengths. A filter layer having wavelength selectivitythrough optical transmittance or absorptance may alternatively be formedin addition to the first buffer layer 17.

In a case where a plurality of servo layers are formed in an opticalrecording medium as in the conventional arrangement, rules as to whichservo layer is used and on which recording and reading layer recordingis performed, for example, are complicated and a disorder can occur inrecording and reading control. Recording/reading control can besimplified if only the tracking beam 270A from the first optical pickup90A is applied to one servo layer 18, as in the present embodiment, andif recording is performed on all the layers in the first and secondrecording and reading layer groups 14 and 34 by using a tracking errorsignal from the first optical pickup 90A. As a result, the occurrence ofrecording and reading errors can also be reduced.

A case where the thicknesses of the first cover layer 11 and the secondcover layer 31 in the optical recording medium 10 in the above-describedembodiment are set equal to each other has been described by way ofexample. However, the present invention is not limited to this. Forexample, it is also preferable that the first cover layer 11 and thesecond cover layer 31 have different thicknesses, as in an opticalrecording medium 10 shown in FIG. 29. More specifically, the thicknessof the first cover layer 11 is set larger than that of the second coverlayer 31 by an amount corresponding to the thickness of the supportsubstrate 12. By this setting, the servo layer 18 is set at the centerin the thickness direction of the optical recording medium 10. When thisoptical recording medium 10 is made, it is preferable that the firstcover layer 11 and the second cover layer 31 differing in thickness beformed. Even if these layers are not stacked simultaneously with eachother, a certain degree of rigidity is already secured by the supportsubstrate 12, the first and second buffer layers 17 and 37, the firstrecording and reading layer group 14, the first intermediate layer group16, the second recording and reading layer group 34 and the secondintermediate layer group 36, thereby sufficiently limiting warpage anddeformation of the optical recording medium 10.

Further, the embodiment has been described only with respect to a casewhere recording film is formed in advance as each recording and readinglayer in the first and second recording and reading groups 14 and 34.However, the present invention is not limited to this. For example, thewhole of regions that can be formed as the first and second recordingand reading layer groups afterwards can be formed as first and secondbulk layers 13 and 33 having a predetermined thickness, as in an opticalrecording medium 10 shown in FIG. 30. When the recording beams 170A and170B are applied to the first and second bulk layers 13 and 33, statechanges are caused only in the portions to which the focal points of thebeam spots are applied, thereby forming recording marks. That is, theoptical recording medium according to the present invention is notlimited to ones in which recording and reading layers to which a beam isapplied are formed in advance. The optical recording medium according tothe present invention includes one in which recording marks are formedin a planar region as occasion arises to form first and second recordingand reading layer groups 14 and 34 in multilayer form as sets of therecording marks after the medium is produced. Use of the structure ofthe bulk layers 13 and 33 in the optical recording medium 10 enablesfreely setting the positions of recording and reading layers within theregions of the bulk layers 13 and 33. For example, even if thethicknesses and the locations of the first and second bulk layers 13 and33 are different from each other, the distances between the first andsecond recording and reading layer groups 14 and 34 and the first andsecond surfaces 10A and 30A can be set equal to each other. While astructure formed without cover layers when the first and second bulklayers 13 and 33 are used has been described, the buffer layers may alsobe removed.

The present embodiment has been described by way of example with respectto a case where information is recorded by applying the recording andreading beams 170A and 170B to the first and second recording andreading layer groups 14 and 34 while tracking control is being performedby applying the tracking beam 270A from the first optical pickup 90A tothe servo layer 18. However, the present invention is not limited tothis. For example, an arrangement can also be adopted in which, as shownin FIG. 31, a tracking beam 270B is also provided in the second opticalpickup 90B and the first and second optical pickups 90A and 90B areindependently controlled in tracking by applying the tracking beams 270Aand 270B from opposite sides to the servo layer 18. With thisarrangement, simultaneously performing recording in different places inthe first and second recording and reading layer groups 14 and 34 isalso enabled.

The present embodiment has been described with respect to a case whereno concavo-convex pattern for tracking control are formed in the firstand second recording and reading layers 14 and 34. However, the presentinvention is not limited to this. A concavo-convex pattern for trackingmay be formed in each of the first and second recording and readinglayers 14 and 34.

The present embodiment has been described by way of example with respectto a case where the output control device 86 performs OPC control on thetrial writing area to select the optimum recording power and performscontrol by directly transmitting this recording power to the recordingpower adjusting means 89. However, the present invention is not limitedto this. For example, it is also preferable to correct by addition ormultiplication the optimum recording power obtained by OPC control andto transmit the corrected optimum recording power to the recording poweradjusting means 89. More specifically, it is preferable to makedetermination, at the time of determining the recording power for aparticular one of the recording and reading layers, as to whether or notinformation is recorded in another of the recording and reading layersexisting closer to the light incident surface side relative to theparticular recording and reading layer, and to correct the recordingpower for the particular recording and reading layer based on thisdetermination. For example, if the transmittance to the recording beamis reduced by recording information in the recording and reading layeron the light incident surface side of the particular recording andreading layer, it is preferable to make a correction such that theoptimum recording power at the time of recording information in theparticular recording and reading layer. In this way, the recordingquality can be further improved.

The present embodiment has been described by way of example with respectto a case where the optimum recording power selected by OPC control isstored in the memory means 87A. However, it is preferable to store thisoptimum recording power in the memory means 87A together with individualidentification information (medium recognition information) of theoptical recording medium 10. In this manner, when the optical recordingmedium 10 is again mounted in the optical recording and readingapparatus 70 after being temporarily taken out of the optical recordingand reading apparatus 70, the output control device 86 can read theindividual identification information about the optical recording medium10 again mounted, refer to the memory means 87A and read the optimumrecording power in the past. As a result, the OPC control time at thetime of changing the optical recording medium 10 can be furthershortened. This optimum recording power can also be stored on theoptical recording medium 10 side by being recorded in a management areaor the like in some of the recording and reading layers of the opticalrecording medium 10.

The present embodiment has been described with respect to a case wherethe wavelength of the tracking beam 270A and the wavelength of therecording and reading beams 170A and 170B are respectively in the redand blue wavelength ranges and different from each other. However, thepresent invention is not limited to this. Beams with wavelengths in thesame wavelength range may be used for tracking and recording andreading.

A sixth embodiment of the present invention will be described below withreference to the accompanying drawings. Note that this sixth embodimentdiffers from the fifth embodiment only in an optical recording andreading method and uses an optical recording medium 10 and an opticalrecording and reading apparatus 70 that are the same as those describedin the fifth embodiment. Therefore, illustration and explanation ofstructures of the medium 10 and the apparatus 70 will be omitted byreferring to FIGS. 19 to 23 for the fifth embodiment.

With the optical recording and reading method according to the sixthembodiment, information is simultaneously recorded to a pair ofrecording and reading layers that are in a first recording and readinglayer group 14 and a second recording and reading layer group 34,respectively, and whose ordinal positions in the layer groups withrespect to a center in a thickness direction of the optical recordingmedium 10 are the same as each other.

<OPC Control>

When information is recorded to the optical recording medium 10,recording powers of the optical recording and reading apparatus 70 arefirst set in accordance with a flowchart in FIG. 32.

First, in step 300, an output control device 86 reproduces a DI (discinformation) area of the optical recording medium 10, thereby readingbasic characteristics information as to the optical recording medium 10.In the DI area, in addition to a type of the medium (a write-once typeor a rewritable type), a recording speed (1×, 2×, or the like), arecording strategy, a position of a servo layer 18, positions ofrecording and reading layers, and inter-layer distances of the recordingand reading layers, a recommended recording power P_(K) of a laser beamis also recorded. Accordingly, the recommended recording power P_(K) isset as an initial recording condition (step 302). Note that in thisembodiment, the ID area is formed on the servo layer 18. Consequently,the information is read from the servo layer 18 with a beam 270A in ared wavelength range of a first optical pickup 90A.

Next, in step 304, it is judged to which recording and reading layers inthe first and second recording and reading layer groups 14 and 34 of theoptical recording medium 10 information is to be recorded. Morespecifically, it is judged whether recording and reading layers, whichare a pair of recording targets, are layers, whose ordinal positions arethe even-number-th when counted from a center side in the thicknessdirection of the optical recording medium 10, or layers, whose ordinalpositions are the odd-number-th when counted from the center side. Forinstance, when simultaneous recording is to be performed to an L0recording and reading layer 14A in the first recording and reading layergroup 14 and an L0 recording and reading layer 34A in the secondrecording and reading layer group 34, it is judged that the recordingtargets are layers whose ordinal positions are the odd-number-th (firstposition), so the procedure proceeds to step 306. On the other hand,when the simultaneous recording is to be performed to an L1 recordingand reading layer 14B in the first recording and reading layer group 14and an L1 recording and reading layer 34B in the second recording andreading layer group 34, it is judged that the recording targets arelayers whose ordinal positions are the even-number-th (second position),so the procedure proceeds to step 310.

Here, assuming a case where information is to be simultaneously recordedto the L0 recording and reading layers 14A and 34A whose ordinalpositions are the odd-number-th, the procedure proceeds to step 306where a power setting pattern (random pattern, in this case) is recordedin a trial writing area X of the L0 recording and reading layer 34A inthe second recording and reading layer group 34 (see FIG. 33). Whendoing so, as already described with reference to FIG. 26 in the fifthembodiment, by strengthening and weakening a recording power for actualrecording with reference to the recommended recording power P_(K) in amulti-step manner (P_(K+1), P_(K+2), P_(K+3), P_(K−1), P_(K−2), andP_(K−3)), work for writing the power setting pattern is executed foreach recording power. Note that a concrete method used to record thepower setting pattern in the trial writing area X of the L0 recordingand reading layer 34A will be described in detail later in anexplanation of a second recording and reading operation, so itsexplanation will be omitted here.

Following this, in step 308, a not specifically illustrated PRMLprocessing device reproduces the recorded power setting pattern and, instep 314, quality evaluating means 88 evaluates quality of a readingsignal using an error rate or SAM value of the reproduced pattern. Aresult of the evaluation is transmitted to trial writing means 87. Instep 316, the trial writing means 87 finds a recording power with whichrecording having the highest quality was performed, determines recordingpowers Pw, erasing powers Pe, and bias powers Pb of both of a lightsource 101A of the first optical pickup 90A and a light source 101B of asecond optical pickup 90B with reference to the found recording power,and instructs recording power adjusting means 89 of the determinedpowers. Through the steps described above, the recording power settingis completed. Note that the recording power adjusting means 89 controlsboth of the light source 101A of the first optical pickup 90A and thelight source 101B of the second optical pickup 90B using the instructedrecording powers Pw, erasing powers Pe, and bias powers Pb.

On the other hand, when it is judged in step 304 that the simultaneousrecording is to be performed to the L1 recording and reading layers 14Band 34B whose ordinal positions are the even-number-th, the procedureproceeds to step 310 where a power setting pattern (random pattern, inthis case) is recorded in a trial writing area X of the L1 recording andreading layer 14B in the first recording and reading layer group 14 (seeFIG. 33). Note that a concrete method used to record the power settingpattern in the trial writing area X of the L1 recording and readinglayer 14B will be described in detail later in an explanation of a firstrecording and reading operation, so its explanation will be omittedhere.

Then, in step 312, a not specifically illustrated PRML processing devicereproduces the recorded power setting pattern. Like in the case of thelayers whose ordinal positions are the odd-number-th, in step 314, thequality evaluating means 88 evaluates quality of a reading signal and,in step 316, the trial writing means 87 determines the recording powersPw, erasing powers Pe, and bias powers Pb of both of the light source101A of the first optical pickup 90A and the light source 101B of thesecond optical pickup 90B. In this manner, OPC is completed.

<Simultaneous Recording of Information in First and Second Groups ofRecording and Reading Layers>

As already described, in this embodiment, information is simultaneouslyrecorded to or reproduced from recording and reading layers that are inthe first recording and reading layer group 14 and the second recordingand reading layer group 34, respectively, and whose ordinal positions inthe layer groups with respect to the center in the thickness directionof the optical recording medium 10 are the same as each other. Morespecifically, when recording of information to the L0 recording andreading layer 14A in the first recording and reading layer group 14 isperformed as the first recording and reading operation, tracking isfirst performed by applying the beam 270A in the red wavelength range ofa tracking optical system 200A of the first optical pickup 90A to theservo layer 18. More concretely, as shown in FIG. 34, the tracking isperformed by applying a spot of the beam 270A to both of grooves 18B andlands 18A of the servo layer 18. Concurrently with the tracking, arecording beam 170A in a blue wavelength range of a recording andreading optical system 100A of the first optical pickup 90A is appliedto the L0 recording and reading layer 14A.

As a result, while tracking the grooves 18B and the lands 18A,information is recorded to the L0 recording and reading layer 14A alongthe grooves 18B and the lands 18A. Consequently, track pitches P2 ofrecording marks formed on the L0 recording and reading layer 14A becomea half of pitches P1 between the grooves 18B.

Also, when recording of information to the L0 recording and readinglayer 34A in the second recording and reading layer group 34 isperformed as the second recording and reading operation, trackingcontrol of the second optical pickup 90B is performed using a trackingerror signal of the tracking optical system 200A of the first opticalpickup 90A. As a result, positions of the first optical pickup 90A andthe second optical pickup 90B with respect to a tracking directionalways coincide with each other. Concurrently with the tracking, arecording beam 170B in the blue wavelength range of a recording andreading optical system 100B of the second optical pickup 90B is appliedto the L0 recording and reading layer 34A. As a result, information isrecorded to the L0 recording and reading layer 34A. Track pitches P2 ofrecording marks formed on the L0 recording and reading layer 34A alsobecome a half of the pitches P1 between the grooves of the servo layer18.

By concurrently carrying out the above-described first recording andreading operation and second recording and reading operation,simultaneous recording of information to the first and second recordingand reading layer groups 14 and 34 is achieved.

It should be noted that the recording powers Pw, erasing powers Pe, andbias powers Pb used to perform the simultaneous recording are those setby the OPC control using the L0 recording and reading layer 34A in thesecond recording and reading layer group 34 in the already describedmanner.

After recording of necessary information to the L0 recording and readinglayer 14A in the first recording and reading layer group 14 and the L0recording and reading layer 34A in the second recording and readinglayer group 34 is completed, additional information as to this recording(address information, content information, and the like concerning therecording) is simultaneously recorded to management areas that arereserved in advance in parts of the L0 recording and reading layers 14Aand 34A.

Following this, when the information recording to the L0 recording andreading layers 14A and 34A is resumed, the management areas of the L0recording and reading layers 14A and 34A are first reproduced to confirmpositions, at which the recording was previously ended, and therecording is continued from the positions. In this manner, untilinformation recording to the entire data areas of the L0 recording andreading layers 14A and 34A is completed, the recording work issimultaneously continued.

When the recording to the data areas of the L0 recording and readinglayers 14A and 34A is finished, as shown in FIG. 35, recording to dataareas of L1 recording and reading layers 14B and 34B adjacent to the L0recording and reading layers 14A and 34A is started. When doing so, theOPC control is performed using the L1 recording and reading layer 14B inthe first recording and reading layer group 14 in the already describedmanner, thereby setting the recording powers Pw, erasing powers Pe, andbias powers Pb of both of the beams 170A and 170B used to perform thesimultaneous recording.

After recording of necessary information to the Ll recording and readinglayer 14B is completed, additional information as to this recording(address information, content information, and the like concerning therecording) is recorded in the management area of the L0 recording andreading layer 14A described above. By repeating the recording operation,information is simultaneously recorded to each pair of recording andreading layers that are in the first and second recording and readinglayer groups 14 and 34, respectively, and whose ordinal positions in thelayer groups with respect to the center side in the thickness directionof the optical recording medium 10 are the same as each other. Note thatin this embodiment, a case has been described in which information isrecorded by sequentially changing the recording targets from innermostrecording and reading layers to outermost recording and reading layerswith respect to the thickness direction of the optical recording medium10 as indicated by arrows Q in FIG. 35, but the recording may beperformed in an opposite direction by sequentially changing therecording targets from the outermost recording and reading layers to theinnermost recording and reading layers. Also, the recording may beperformed by randomly selecting the ordinal positions of the recordingand reading layers that are the recording targets.

It should be noted that in this embodiment, a case where the managementareas are reserved on the L0 recording and reading layers 14A and 34Ahas been described as an example but other recording and reading layersmay be used instead. Also, when the servo layer 18 includes a recordingfilm, it is preferable that a management area is reserved on the servolayer 18 and additional information is recorded in the area. It issufficient that this recording is performed using the beam 270A for thetracking control. By collectively recording management information onthe servo layer 18, it also becomes possible to simultaneously graspmanagement information as to both of the first recording and readinglayer group 14 and the second recording and reading layer group 34.

Also, no specific example has been described in this embodiment but wheninformation is continuously recorded across the L0 recording and readinglayers 14A and 34A and the L1 recording and reading layers 14B and 34B,it is preferable that the OPC control is performed in advance for bothof the L0 recording and reading layer 34A, whose ordinal position is theodd-number-th, and the L1 recording and reading layer 14B, whose ordinalposition is the even-number-th, and each recording power is set in amemory. By doing so, it becomes possible to maintain continuity of aninformation transfer rate.

<Simultaneous Reproducing of Information from First and Second Groups ofRecording and Reading Layers>

In this embodiment, information simultaneously recorded to the firstrecording and reading layer group 14 and the second recording andreading layer group 34 is simultaneously reproduced. For instance, asshown in FIG. 36, when reproducing of information from the L0 recordingand reading layer 14A in the first recording and reading layer group 14is performed as a first reproducing operation, the beam 170A of therecording and reading optical system 100A of the first optical pickup90A is applied to the L0 recording and reading layer 14A, therebyperforming the reproducing while performing tracking control and focuscontrol.

Also, when reproducing of information from the L0 recording and readinglayer 34A in the second recording and reading layer group 34 isperformed as a second reproducing operation, the beam 170B of therecording and reading optical system 100B of the second optical pickup90B is applied to the L0 recording and reading layer 34A, therebyperforming the reproducing while performing tracking control and focuscontrol. By concurrently carrying out the first reproducing operationand the second reproducing operation, simultaneous reproducing ofinformation from the first and second recording and reading layer groups14 and 34 is achieved. Note that, at the time of recording, trackingcontrol is performed using the servo layer 18 but, on the occasion ofsimultaneous reproducing, the first and second optical pickups 90A and90B are tracking-controlled independently of each other using therecording and reading optical systems 100A and 100B, respectively.

With the above-described optical recording and reading method accordingto the sixth embodiment, by simultaneously executing the first recordingand reading operation using the first optical pickup 90A and the secondrecording and reading operation using the second optical pickup 90B,information is simultaneously recorded to or reproduced from the firstand second recording and reading layer groups 14 and 34. As a result, itbecomes possible to dramatically enhance a transfer rate at the time ofrecording or reading.

In particular, with the optical recording and reading method in thisembodiment, the first recording and reading layer group 14 and thesecond recording and reading layer group 34 each include a plurality ofrecording and reading layers, with the number of the recording andreading layers in the first recording and reading layer group 14 andthat in the second recording and reading layer group 34 being set thesame as each other, and information is simultaneously recorded to orreproduced from a pair of recording and reading layers whose ordinalpositions with respect to the center in the thickness direction of theoptical recording medium 10 are the same as each other. By doing so,distances of recording and reading layers, which are a pair of recordingand reading targets, from surfaces 10A and 30A of the optical recordingmedium 10 become closely analogous to each other and optical paths ofthe beams assume a symmetric state. As a result, for instance, itbecomes possible to use a control signal (more specifically, controlinformation concerning tilting, surface runout, and the like of theoptical recording medium 10) obtained at the first optical pickup 90A asa control signal for the second optical pickup 90B as it is by reversinga polarity of the information. Consequently, it also becomes possible toomit, from the second optical pickup 90B, a special photodiode mechanismand the like for obtaining the control signal.

Also, in this embodiment, at the time of changing the recording andreading targets to other recording and reading layers, it is sufficientthat focuses of the beams 170A and 170B of the first and second opticalpickups 90A and 90B are moved symmetrically with reference to the centerof the optical recording medium 10. Such control of the beam focusesenables smooth changing to another pair of recording and reading layerswhose ordinal positions with respect to the center in the thicknessdirection of the optical recording medium 10 are the same as each other.As a result, it becomes possible to simplify control of inter-layerjump.

Further, information is simultaneously recorded to a pair of recordingand reading layers whose ordinal positions in the first and secondrecording and reading layer groups 14 and 34 with respect to the centerin the thickness direction of the optical recording medium 10 are thesame as each other, so recording characteristics to the pair of therecording and reading layers become closely analogous to each other.Accordingly, in this embodiment, when information is simultaneouslyrecorded to a pair of recording and reading layers, the OPC is performedusing only one of the recording and reading layers. Consequently, itbecomes possible to, as compared with a case where the OPC is performedfor both of the first and second recording and reading layer groups 14and 34, halve a time taken by the OPC.

Still further, in this embodiment, as shown in FIG. 33, when recordingis performed to recording and reading layers whose ordinal positions inthe first and second recording and reading layer groups 14 and 34 arethe even-number-th when counted from the center side of the opticalrecording medium 10, the OPC is performed using the first recording andreading layer group 14 and when recording is performed to recording andreading layers whose ordinal positions in the first and second recordingand reading layer groups 14 and 34 are the odd-number-th when countedfrom the center side, the OPC is performed using the second recordingand reading layer group 34. As a result, the trial writing areas X inthe first recording and reading layer group 14 are formed only onrecording and reading layers, whose ordinal positions are theeven-number-th, and the trial writing areas X in the second recordingand reading layer group 34 are formed only on recording and readinglayers whose ordinal positions are the odd-number-th. Accordingly, thereoccurs no overlapping of the trial writing areas X between adjacentrecording and reading layers, so occurrence of noise at the time of theOPC is suppressed, which makes it possible to, even when the inter-layerdistances of the recording and reading layers are reduced, enhanceaccuracy of the OPC. Also, the trial writing areas X are not adjacent toeach other, so even when there occurs overlapping in a layered directionof random data recorded in the OPC, accuracy of the OPC is hard todeteriorate, which makes it possible to decrease the trial writing areasX. As a result, it becomes possible to increase user data areas of thefirst and second recording and reading layer groups 14 and 34.

Now, a seventh embodiment of the present invention will be describedwith reference to the accompanying drawings. In the seventh embodiment,except an optical recording and reading method, the same opticalrecording medium 10 and optical recording and reading apparatus 70 asthose in the fifth embodiment are used.

Thus, showing and descriptions of these structures will be fully omittedby referring to FIGS. 19 to 23 of the fifth embodiment.

<Simultaneous Recording of Information in First and Second Groups ofRecording and Reading Layers>

In the seventh embodiment, information is simultaneously recorded on afirst group of recording and reading layers 14 and a second group ofrecording and reading layers 34. Specifically, as a first recordingoperation, in order to record information on an L0 recording and readinglayer 14A of the first group of recording and reading layers 14, a beam270A in a red wavelength range from a tracking optical system 200A of afirst optical pickup 90A is first applied to a servo layer 18 to performtracking. Specifically, as shown in FIG. 37, a spot of the beam 270A isapplied to a groove 18B and a land 18A in the servo layer 18 to performtracking. Simultaneously with the tracking, a recording beam 170A in ablue wavelength range from a recording and reading optical system 100Aof the first optical pickup 90A is applied to the L0 recording andreading layer 14A.

Thus, with both the groove 18B and the land 18A being tracked,information is recorded on the L0 recording and reading layer 14A alongthe groove 18B and the land 18A. Thus, a track pitch P2 of a recordingmark formed on the L0 recording and reading layer 14A is a half of apitch P1 between the grooves 18B or between the lands 18A.

As a second recording operation, when information is recorded on an L0recording and reading layer 34A of the second group of recording andreading layers 34, tracking control of a second optical pickup 90B isperformed using a tracking error signal from the tracking optical system200A of the first optical pickup 90A. Thus, the first optical pickup 90Aand the second optical pickup 90B are always located in the sameposition in a tracking direction. Simultaneously with the tracking, arecording beam 170B in a blue wavelength range from a recording andreading optical system 100B of the second optical pickup 90B is appliedto the L0 recording and reading layer 34A. Thus, information is recordedon the L0 recording and reading layer 34A. A track pitch P2 of arecording mark formed on the L0 recording and reading layer 34A is alsoa half of the pitch P1 between the grooves 18B or between the lands 18Ain the servo layer 18. The first recording operation and the secondrecording operation are concurrently advanced to achieve simultaneousrecording of information on the first and second groups of recording andreading layers 14 and 34.

On the servo layer 18, information on basic specifications of theoptical recording medium 10 or the number of layers of the first groupsof recording and reading layers 14 are previously recorded in arecording pit or a BCA (burst cutting area), and is always read by thebeam 270A in the red wavelength range before start of the trackingcontrol. Basic information on the optical recording medium includes theposition of the servo layer 18, the position of each recording andreading layer, a rule on an inter-layer distance of the group ofrecording and reading layers.

After necessary information is recorded on the L0 recording and readinglayer 14A of the first group of recording and reading layers 14 and theL0 recording and reading layer 34A of the second group of recording andreading layers 34, the current additional information (addressinformation on recording, contents information, or the like) issimultaneously recorded in management areas previously ensured on the L0recording and reading layers 14A and 34A.

Then, when recording of information on the L0 recording and readinglayers 14A and 34A is restarted, the management areas on the L0recording and reading layers 14A and 34A are first reproduced to checkthe positions where the previous recording has been completed, andrecording is continued from the positions. As such, a recordingoperation is simultaneously continued until recording of information inall data areas on the L0 recording and reading layers 14A and 34A iscompleted.

After recording in the data areas on the L0 recording and reading layers14A and 34A is completed, as shown in FIG. 38, recording is started indata areas on L1 recording and reading layers 14B and 34B adjacent tothe L0 recording and reading layers 14A and 34A. After recording ofnecessary information on the L1 recording and reading layer 14B iscompleted, the current additional information (address information onrecording, contents information, or the like) is recorded in themanagement area on the previous L0 recording and reading layer 14A. Sucha recording operation is repeated, and thus information issimultaneously recorded on the pair of recording and reading layers inthe same ordinal position in the first and second groups of recordingand reading layers 14 and 34. In particular, in this embodiment,information is recorded in order from a central side toward an outerside in a thickness direction of the optical recording medium 10 asshown by arrow Q in FIG. 38.

The case where the management areas are ensured in the L0 recording andreading layers 14A and 34A has been exemplified, but another recordingand reading layer may be used. In the case where the servo layer 18includes a recording film, it is preferable that a management area isensured on the servo layer 18, and additional information is recordedtherein. This recording may be performed using the beam 270A performingthe tracking control. The management information is concentrated on theservo layer 18, and thus management information on both the first groupof recording and reading layers 14 and the second group of recording andreading layers 34 can be simultaneously grasped.

<Simultaneous Reproducing of Information from First and Second Groups ofRecording and Reading Layers>

In this embodiment, information simultaneously recorded on the firstgroup of recording and reading layers 14 and the second group ofrecording and reading layers 34 is simultaneously reproduced. Forexample, as shown in FIG. 39, as a first reproducing operation, wheninformation on the L0 recording and reading layer 14A of the first groupof recording and reading layers 14 is reproduced, the beam 170A from therecording and reading optical system 100A of the first optical pickup90A is applied to the L0 recording and reading layer 14A to reproducethe information while performing tracking control and focus control.

As a second reproducing operation, when information on the L0 recordingand reading layer 34A of the second group of recording and readinglayers 34 is reproduced, the beam 170B from the recording and readingoptical system 100B of the second optical pickup 90B is applied to theL0 recording and reading layer 34A to reproduce the information whileperforming tracking control and focus control. The first reproducingoperation and the second reproducing operation are concurrently advancedto achieve simultaneous reproducing of the information on the first andsecond group of recording and reading layers 14 and 34. The trackingcontrol is performed using the servo layer 18 during recording, buttracking control of the first and second optical pickups 90A and 90B isseparately performed using the recording and reading optical systems100A and 100B, respectively, during simultaneous reproducing.

AS described above, according to the optical recording and readingmethod of this embodiment, while the tracking beam 270A is being appliedto the servo layer 18 to perform tracking control, the recording andreading beam 170A of the first optical pickup 90A is applied to thefirst group of recording and reading layers 14 to record information(first recording operation). Meanwhile, the beam 270A and the servolayer 18 used in the first recording and reading operation are used toperform tracking control of the second optical pickup 90B, and therecording and reading beam 170B of the second optical pickup 90B isapplied to the second group of recording and reading layers 34 to recordinformation (second recording operation). Thus, in the second opticalpickup 90B in the optical recording and reading apparatus 70, a trackingoptical system can be omitted to simplify a structure.

Meanwhile, according to the optical recording and reading method, twoindependent recording and reading beams 170A and 170B can be used torecord information on the first and second groups of recording andreading layers 14 and 34. Thus, a focus movement range of the recordingand reading beams 170A and 170B of the first and second optical pickups90A and 90B can be shared in the thickness direction. Thus, even if thenumber of recording and reading layers is increased, an effective statefor comatic aberration due to a tilt or the like can be brought.

Specifically, in the optical recording and reading method, the recordingand reading beam 170A of the first optical pickup 90A used in the firstrecording operation is incident on the first surface 10A of the opticalrecording medium 10, and the recording and reading beam 170B of thesecond optical pickup 90B used in the second recording operation isincident on the second surface 30A of the optical recording medium 10.As a result, for example, in the first optical pickup 90A that performsthe first recording operation, recording is performed on the firstrecording and reading layer 14 placed on one side with reference to thecenter in the thickness direction of the optical recording medium 10,and in the second optical pickup 90B that performs the second recordingoperation, recording is performed on the second recording and readinglayer 34 placed on the other side with reference to the center in thethickness direction of the optical recording medium 10. Thus, as in theoptical recording medium 10, the first recording and reading layer 14can be brought close to the first surface 10A, and the second group ofrecording and reading layers 34 can be brought close to the secondsurface 30A. Therefore, according to this recording and reading method,the number of recording and reading layers can be increased, and furtheran effective state for comatic aberration due to a tilt or the like canbe brought.

In the optical recording medium 10 used in this embodiment, the firstgroup of recording and reading layers 14 and the second group ofrecording and reading layers 34 are located symmetrically with respectto the center in the thickness direction of the optical recording medium10. Thus, optical design of the first and second optical pickups 90A and90B in the optical recording and reading apparatus 70, positionalrecognition of the recording and reading layer, focus control, or thelike can be made uniform to increase a recording and reading speed.Internal stress generated in the first and second groups of recordingand reading layers 14 and 34 in the optical recording medium 10 is alsosymmetrical in the thickness direction, thereby preventing warpage ofthe optical recording medium 10.

Further, in the optical recording and reading method, the firstrecording operation using the first optical pickup 90A and the secondrecording operation using the second optical pickup 90B aresimultaneously performed to simultaneously record information on thefirst and second groups of recording and reading layers 14 and 34,thereby rapidly increasing a transfer rate during recording.

In the optical recording and reading method, the recording and readingbeam 170A of the first optical pickup 90A and the recording and readingbeam 170B of the second optical pickup 90B are located circumferentiallyaway from each other with respect to the optical recording medium 10.Thus, even if the beams 170A and 170B pass through opposite surfaces, aharmful effect on a reproduction waveform can be avoided. If a largeamount of tracking beam 270A applied to the servo layer 18 passesthrough the servo layer 18, the second optical pickup 90B may receive aharmful effect. Thus, in the optical recording medium 10, transmittanceof the beam 270A through the servo layer 18 is set to 10% or less toprevent a harmful effect of the beam 270A on the second optical pickup90B.

Further, in the optical recording and reading method, a plurality offirst groups of recording and reading layers 14 and a plurality ofsecond groups of recording and reading layers 34 are the same in number,and information is simultaneously recorded on recording and readinglayers in the same ordinal position from the center in the thicknessdirection of the optical recording medium 10. Then, for a pair ofrecording and reading layers as recording targets, distances from thesurfaces 10A and 30A of the optical recording medium 10 are approximate,and optical paths of the beams are also symmetrical. Thus, for example,a control signal obtained in the first optical pickup 90A, specifically,control information of a tilt or runout of the optical recording medium10 can be used as a control signal of the second optical pickup 90B bychanging the polarity of the information. As a result, in the secondoptical pickup 90B, a special photodiode mechanism or the like forobtaining the control signal can be omitted.

For the optical recording and reading method of the embodiment, the casewhere information is recorded on the first and second groups ofrecording and reading layers 14 and 34 in layer order from the centralside toward the outer side in the thickness direction of the opticalrecording medium 10 has been exemplified, but the present invention isnot limited to this. For example, information may be recorded on thefirst and second groups of recording and reading layers 14 and 34 instacking order from the outer side toward the central side of theoptical recording medium 10. Also, a pair of recording and readinglayers in the same ordinal position may be extracted from the first andsecond groups of recording and reading layers 14 and 34 at random forrecording.

As in the optical recording medium 10 shown in FIG. 40, thicknesses ofthe first and second buffer layers 17 and 37 may be changed, orinter-layer distances or the numbers of layers of the first and secondgroup of recording and reading layers 14 and 34 may be changed to locatethe servo layer 18 at the center in the thickness direction.

Further in this embodiment, the case where the first group of recordingand reading layers 14 and the second group of recording and readinglayers 34 are placed on the sides of the opposite surfaces 10A and 30Aof the optical recording medium 10 has been described, but the presentinvention is not limited to this. For example, as shown in FIG. 41, boththe first group of recording and reading layers 14 and the second groupof recording and reading layers 34 may be placed with divided regions inthe thickness direction on the side of one surface 10A of the opticalrecording medium 10. In this case, recording and reading is performed onthe first group of recording and reading layers 14 using the beam 170Aof the first optical pickup 90A, and recording and reading is performedon the second group of recording and reading layers 34 using the beam170B of the second optical pickup 90B. Tracking control of the firstoptical pickup 90A and the second optical pickup 90B are performed byapplying the common beam 270A to the servo layer 18. The recording andreading layers are shared by the plurality of recording and readingbeams 170A and 170B, thereby reducing influences of comatic aberrationdue to an error in film formation or a tilt, and increasing the numberof recording and reading layers. Also in this case, the servo layer 18may be placed between the first group of recording and reading layers 14and the second group of recording and reading layers 34.

In this embodiment, the case where information is simultaneouslyrecorded on the pair of recording and reading layers using the first andsecond optical pickups 90A and 90B has been exemplified, but the presentinvention is not limited to this. For example, when information isrecorded on the first group of recording and reading layers 14 using therecording and reading beam 170A with the tracking beam 270A beingapplied to the servo layer 18 as in the first recording operation shownin FIG. 42A, the beam 170B of the second optical pickup 90B may bestopped. When information is recorded on the second group of recordingand reading layers 34 using the beam 170B of the second optical pickup90B as in the second recording operation shown in FIG. 42B, only thetracking beam 270A of the first optical pickup may be applied to theservo layer 18 to perform tracking control, and the recording andreading beam 170A may be stopped. This reduces the transfer rate duringrecording and reading, but eliminates the need for informationmanagement for simultaneous recording/simultaneous reproducing, therebysimplifying an information control program for recording and reading.

Now, an eighth embodiment of the present invention will be describedwith reference to the accompanying drawings.

FIGS. 43 to 45 illustrate configurations of an optical recording medium10, and first and second optical pickups 90A and 90B used for therecording and reading of the optical recording medium 10 according tothe eighth embodiment.

The first optical pickup 90A applies a beam to a first surface 10A thatis one side of the optical recording medium 10. The second opticalpickup 90B applies a beam to a second surface 30A that is the other sideof the optical recording medium 10. It should be noted that unlike thefifth embodiment, internal configurations of the first and secondoptical pickups 90A and 90B are substantially the same. That is, asillustrated in FIG. 3, the second optical pickup 90B also includes atracking optical system 200B. Thus, in the following drawings anddescription, A is added to each end of reference numerals of componentsin the first optical pickup 90A, B is added to each end of referencenumerals of components in the second optical pickup 90B, and the othercomponents are denoted by the same reference numerals. Also, becausemain members of the first and second optical pickups 90A and 90B aresimilar or identical to those of the first optical pickup 90 as shown inthe fifth embodiment, an illustration and a description thereof will beomitted and respects different from the fifth embodiment will be mainlydescribed.

In the eighth embodiment, when information is recorded on the firstgroup of recording and reading layers 14 using the recording and readingoptical system 100A, as illustrated in FIG. 44, a TE signal of thetracking optical system 200A is amplified to a desired level and phasecompensated, thereafter being fed to the actuators 191A and 192A toperform tracking control. As a result, the recording and reading opticalsystem 100A records information on the first group of recording andreading layers 14 on the basis of the tracking control of the trackingoptical system 200A. In the present embodiment, when informationrecorded on the first group of recording and reading layers 14 isreproduced, tracking control of the recording and reading optical system100A is independently performed using recording marks on the first groupof recording and reading layers 14. Of course, the information may alsobe reproduced by using tracking control of the tracking optical system200A.

Recording/reading on the second group of recording and reading layers 34is performed in the second optical pickup 90B. As illustrated in FIG.45, when information is recorded on the second group of recording andreading layers 34 using the recording and reading optical system 100B inthe second optical pickup, TE signals obtained by applying the trackingoptical system 200B to the servo layer 18 are used. Using the TEsignals, information is recorded on the second group of recording andreading layers 34 while tracking control of the recording and readingoptical system 100B is being performed.

Therefore, the servo layer 18 of the optical recording medium 10 is usedby both the first and second optical pickups 90A and 90B for the purposeof tracking As a result, the pitch P1 (around 0.64 μm) between the lands18A or between the grooves 18B of the servo layer 18 is a length thatallows sufficient tracking with the beams 270A and 270B in a relativelylong red wavelength range from the first and second optical pickups 90Aand 90B. As a result, the beam 270A of the tracking optical system 200Ain the first optical pickup 90A and the beam 270B of the trackingoptical system 200B in the second optical pickup 90B are guided by theservo layer 18.

It is noted that a second buffer layer 37 formed at the side of thesecond surface 30A in the support substrate 12 of the optical recordingmedium 10 is composed of optically transparent acrylic ultravioletcurable resin and has a film thickness set at 238 μm. Also, a refractiveindex of a second buffer layer 37 in a wavelength condition of thetracking beam 270B is set at a lower refractive index than that of thesupport substrate 12 in the same wavelength. As such, the tracking beam270B incident from the second buffer layer 37 is allowed to smoothlyreach the servo layer 18 through the support substrate 12. In thepresent embodiment, a refractive index of the first buffer layer 17 in awavelength condition of the tracking beam 270A is set at a lowerrefractive index than that of the support substrate 12 in the samewavelength. As such, materials of the second buffer layer 37 and thefirst buffer layer 17 can be made uniform and deposition processes canalso be made uniform.

Further, a material selected for the first and second buffer layers 17and 37 has a larger amount of absorbed light with the shortness of abeam wavelength. As such, an amount of absorbed light of the beams 170Aand 170B in the blue wavelength is large, and an amount of absorbedlight of the beams 270A and 270B in the red wavelength is small. As aresult, since the first and second buffer layers 17 and 37 can reduce anamount of light of the beams 170A and 170B in the blue wavelength thatreach the servo layer 18, signal noises can be reduced at the time ofreproduction. Also, the first and second buffer layers 17 and 37actively transmit the beams 270A and 270B in the red wavelength toincrease an amount of light of tracking signals.

Next, an optical recording and reading method according to the eighthembodiment will be described.

When information is recorded on the L0 recording and reading layer 14Ain the first group of recording and reading layers 14 adjacent to theservo layer 18 of the support substrate 12, first, the beam 270A, in thered wavelength range, of the tracking optical system 200A in the firstoptical pickup 90A is applied to the servo layer 18 to perform tracking.Specifically, as illustrated in FIGS. 47A and 47B, a spot of the beam270A is applied to the groove 18B and the land 18A in the servo layer 18to perform tracking. Simultaneously therewith, the recording beam 170A,in the blue wavelength range, of the recording and reading opticalsystem 100A in the first optical pickup 90A is applied to the L0recording and reading layer 14A.

As a result, with both the groove 18B and the land 18A being tracked,information is recorded on the L0 recording and reading layer 14A alongthe groove 18B and the land 18A. Thus, a track pitch P2 of recordingmarks formed on the L0 recording and reading layer 14A is a half of apitch P1 between the grooves 18B or between the lands 18A. On the servolayer 18, information on basic specifications of the optical recordingmedium 10 or the number of layers of the first groups of recording andreading layers 14 is previously recorded in a recording pit or a BCA(burst cutting area), and is always read by the beam 270A in the redwavelength range before start of the tracking control. Basic informationon the optical recording medium includes the position of the servo layer18, the position of each recording and reading layer, a rule on aninter-layer distance of the group of recording and reading layers.

After necessary information is recorded on the L0 recording and readinglayer 14A, the current additional information (address information onrecording, content information, or the like) is recorded in a managementarea previously ensured on a part of the L0 recording and reading layer14A.

Then, if recording of information on the L0 recording and reading layer14A is restarted, first, the management area on the L0 recording andreading layer 14A is reproduced to confirm a position at which theprevious recording has been completed, and recording is continued fromthe position. In this manner, the recording is continued until therecording of the information in all data areas on the L0 recording andreading layer 14A is completed. When recording on the data area of theL0 recording and reading layer 14A is finished, recording on the dataarea of the L1 recording and reading layer 14B is started. Afternecessary information is recorded on the L1 recording and reading layer14B, the current additional information (address information onrecording, content information, or the like) is recorded in theabove-described management area of the L0 recording and reading layer14A.

<Recording on a Second Group of Recording and Reading Layers>

If information is recorded on the L0 recording and reading layer 34A ofthe second group of recording and reading layers 34 disposed opposite tothe servo layer 18 of the support substrate 12, first, the beam 270B, inthe red wavelength range, of the tracking optical system 200B in thesecond optical pickup 90B is applied to the servo layer 18 through thesupport substrate 12 to perform tracking Specifically, as illustrated inFIGS. 47C and 47D, a spot of the beam 270B is applied to the groove 18Band the land 18A in the servo layer 18 to perform tracking.Simultaneously therewith, the recording beam 170B, in the bluewavelength range, of the recording and reading optical system 100B inthe second optical pickup 90B is applied to the L0 recording and readinglayer 34A.

As a result, with both the land 18A and the groove 18B being tracked,information is recorded on the L0 recording and reading layer 34A alongthe land 18A and groove 18B. Thus, a track pitch P2 of recording marksformed on the L0 recording and reading layer 34A is a half of a pitch P1between the lands 18A or between the grooves 18B. As mentioned above, onthe servo layer 18, information on basic specifications of the opticalrecording medium 10 or the number of layers of the first group ofrecording and reading layers 14 is previously recorded in a recordingpit or a BCA (burst cutting area). Therefore, the information is alwaysread by the beam 270B in the red wavelength range before start of thetracking control.

After necessary information is recorded on the L0 recording and readinglayer 34A, the current additional information (address information onrecording, content information, or the like) is recorded in a managementarea previously ensured on a part of the L0 recording and reading layer34A.

Then, if recording of information on the L0 recording and reading layer34A is restarted, first, the management area on the L0 recording andreading layer 24A is reproduced to confirm a position at which theprevious recording has been completed, and recording is continued fromthe position. In this manner, the recording is continued until therecording of the information in all data areas on the L0 recording andreading layer 34A is completed. When recording on the data area of theL0 recording and reading layer 34A is finished, recording on the dataarea of the L1 recording and reading layer 34B is started. Afternecessary information is recorded on the L1 recording and reading layer34B, the current additional information (address information onrecording, content information, or the like) is recorded in theabove-described management area of the L0 recording and reading layer34A.

The case where the management areas are ensured in the L0 recording andreading layers 14A and 34A has been exemplified, but another recordingand reading layer may be used. In the case where the servo layer 18includes a recording film, it is preferable to ensure a management areaon the servo layer 18 and record additional information therein. Thisrecording may be performed using the beams 270A and 270B performing thetracking control. The management information is concentrated on theservo layer 18, and thus management information on both the first groupof recording and reading layers 14 and the second group of recording andreading layers 34 can be simultaneously grasped.

As hereinbefore discussed, according to the optical recording medium 10of the eighth embodiment, the servo layer 18 is formed on one surface ofthe support substrate 12, and the first group of recording and readinglayers 14 and the second group of recording and reading layers 34 aredisposed on both surfaces of the support substrate 12. As a result,because internal stress generated when the first and second groups ofrecording and reading layers 14 and 34 are formed is dispersed into bothsides of the support substrate 12, warpage and deformation of theoptical recording medium 10 can be prevented. Such dispersion ofinternal stress enables preventing warpage of the optical recordingmedium 10 even if a thickness of the support substrate 12 is set withinthe range of 100 to 1000 μm.

At this time, an attempt to form concavo-convex patterns for tracking onboth sides of the support substrate 12 complicates a process formanufacturing the support substrate 12, so that the accuracy of thesupport substrate 12 tends to be deteriorated. For this reason, in thepresent embodiment, the accuracy is improved by forming a concavo-convexpattern for tracking on one surface of the support substrate 12 tosimplify the manufacture of the support substrate 12. Also, because theservo layer 18 is shared by the first and second groups of recording andreading layers 14 and 34, which sandwich the servo layer 18,concavo-convex patterns for tracking are not needed to be formed on boththe recording and reading layers of the first and second groups ofrecording and reading layers 14 and 34. As a result, the geometricaccuracy of the optical recording medium 10 can be more improved. Sincethe first group of recording and reading layers 14 and the second groupof recording and reading layers 34 are disposed at both sides of thesupport substrate 12, a recording capacity may also be increased.

Further, in this optical recording medium 10, the support substrate 12is composed of an optically transparent material. As a result, the beam270B from the second optical pickup 90B can be applied to the servolayer 18 through the support substrate 12. If the support substrate 12is composed of an opaque material, tracking control of the secondoptical pickup 90B may be performed using return light of the beam 270Afrom the first optical pickup 90A.

Also, the first group of recording and reading layers 14 and the secondgroup of recording and reading layers 34 of the optical recording medium10 are stacked symmetrically with respect to the center of the supportsubstrate 12 in the thickness direction. Therefore, internal stressgenerated in the first and second groups of recording and reading layers14 and 34 is also symmetrical, so that warpage of the optical recordingmedium 10 can be prevented.

In the optical recording medium 10, a refractive index of the supportsubstrate 12 in a wavelength condition of the tracking beam 270B is setat a higher refractive index than that of the second buffer layer 37 inthe same wavelength. As such, a focus point of the tracking beam 270Bincident from the second buffer layer 37 is allowed to smoothly reachthe servo layer 18 through the support substrate 12. As a result, it isensured that the tracking control of the second optical pickup 90B canbe performed.

Further, in the optical recording medium 10, the reflectance of theservo layer 18 to the tracking beams 270A and 270B in the red wavelengthis set to be greater than that to the recording and reading beams 170Aand 170B. In order to embody this, a material used for the first andsecond buffer layers 17 and 37 has a larger amount of absorbed lightwith the shortness of a beam wavelength. Then, even if the recording andreading beams 170A and 170B in the blue wavelength are incident on theside of the servo layer 18, the incident beams are easily absorbed bythe first and second buffer layers 17 and 37, so that an amount of lightthat reaches the servo layer 18 (an amount of reflected light from theservo layer 18) can be reduced. On the other hand, since the trackingbeams 270A and 270B in the red wavelength can be actively transmittedthrough the first and second buffer layers 17 and 37, an amount of lightthat reaches the servo layer 418 (an amount of reflected light from theservo layer 18) can be increased. As a result, the quality of readingsignals can be improved, as well as stable tracking control can beprovided.

In the present embodiment, the first and second buffer layers 17 and 37have characteristics that light absorptivities are different between thered and blue wavelengths, resulting in different reflectances of theservo layer 18 between the tracking beam and the recording and readingbeam, but the present invention is not limited thereto. For example, areflecting film itself formed on the servo layer 18 may have wavelengthselectivity that reflectance is dependent on a wavelength. Also, inaddition to the first and second buffer layers 17 and 37, a filter layerhaving wavelength selectivity of optical transmittance and absorptancemay be formed.

Further, if a plurality of servo layers are formed in an opticalrecording medium as in a conventional manner, decision of which of theservo layers is used to record information on which of recording andreading layers is complex, so that recording and reading control tendsto be confused. Thus, like the present embodiment, if one servo layer 18is shared by the first group of recording and reading layers 14 and thesecond group of recording and reading layers 34, recording and readingcontrol is simplified, so that the number of recording and readingerrors may be reduced.

It should be noted that in the foregoing embodiment, the case where thethicknesses of the first cover layer 11 and the second cover layer 31are the same has been exemplified, but the present invention is notlimited thereto. For example, like the optical recording medium 10illustrated in FIG. 48, it is also preferable that thicknesses of thefirst cover layer 11 and the second cover layer 31 be different fromeach other. Specifically, a thickness of the first cover layer 11 isincreased to be greater than that of the second cover layer 31 by athickness of the support substrate 12. As such, the servo layer 18 isdisposed at the center of the optical recording medium 10 in a thicknessdirection. As a result, in the first optical pickup 90A and the secondoptical pickup 90B, focal lengths of the tracking optical systems 200Aand 200B are enabled to match each other. When the optical recordingmedium 10 is manufactured, it is preferable to separately stack thefirst cover layer 11 and the second cover layer 31 with differentthicknesses. Even if the first and second cover layers 11 and 31 are notsimultaneously stacked, since some degree of rigidity has been ensuredby the support substrate 12, the first and second buffer layers 17 and37, the first group of recording and reading layers 14 and first groupof intermediate layers 16, and the second group of recording and readinglayers 34 and second group of intermediate layers 36, warpage anddeformation of the optical recording medium 10 can be sufficientlyprevented.

Also, like the optical recording medium 10 shown in FIG. 49, thicknessesof the first and second buffer layers 17 and 37 may be changed, orinter-layer distances or the numbers of layers of the first and secondgroup of recording and reading layers 14 and 34 may be changed to locatethe servo layer 18 at the center in the thickness direction.

Also, each refractive index of the first cover layer 11 and the secondcover layer 31 may be changed, or a refractive index between the firstand second groups of recording and reading layers 14 and 34 may bechanged to locate the servo layer 18 at the center as an opticaldistance in the thickness direction.

Further, in the foregoing embodiment, the case where recording films arepreviously deposited as recording and reading layers of the first andsecond groups of recording and reading layers 14 and 34 has beendescribed, but the present invention is not limited thereto. Forexample, like the optical recording medium 10 illustrated in FIG. 50, anentire area that might become first and second group of recording andreading layers can be first and second bulk layers 13 and 33 having apredetermined thickness. If recording beams 170A and 170B are applied tothe first and second bulk layers 13 and 33, the state of only a focusarea of a beam spot is changed to form a recording mark. That is, in anoptical recording medium according to the present invention, recordingand reading layers to which beam are applied may not be previouslyformed, and recording marks are formed on a planar area at any time, thefirst and second groups of recording and reading layers 14 and 34 may bepost-multi-layered as collections of the recording mark. If thestructure of the bulk layers 13 and 33 is adopted as the opticalrecording medium 10, positions of recording and reading layers may befreely set within the bulk layers 13 and 33. For example, as illustratedin FIG. 50, even if the first bulk layer 13 and the second bulk layer 33have different thicknesses or arrangements, distances from the first andsecond groups of recording and reading layers 14 and 34 to the first andsecond surfaces 10A and 30A are allowed to match each other.

It should be noted that here, the structure in which a cover layer isomitted when the first and second bulk layers 13 and 33 are adopted hasbeen exemplified, but a buffer layer may also be omitted.

A ninth embodiment of the present invention will be described below withreference to the attached drawings. An optical recording medium and anoptical recording and reading apparatus of the ninth embodiment arepartially identical or similar to those of the fifth embodiment, andthus, a description of such parts will be omitted, and the descriptionwill be given focusing on differences from the fifth embodiment.

FIGS. 51 to 54 illustrate an internal configuration of an opticalrecording medium 10 to which an optical recording and reading method ofthe ninth embodiment of the present invention is applied and an internalconfiguration of an optical recording and reading apparatus 70 forachieving the optical recording and reading method. The recording andreading apparatus 70 includes first and second optical pickups 90A and90B, first and second linear motion mechanisms 75A and 75B that move thefirst and second optical pickups 90A and 90B in a tracking direction,and a tracking control device 80 that controls the first and secondlinear motion mechanisms 75A and 75B. Reference numeral 86 denotes adigital signal processing device to/from which user information to berecorded or reproduced is input/output from/to an external informationappliance, and controls data recorded on or data reproduced from theoptical recording medium 10. Although not specifically illustrated, thefirst optical pickup 90A and the second optical pickup 90B have opticalaxes corresponding to each other.

As illustrated in FIG. 52, the first optical pickup 90A includes arecording and reading optical system 100A and a tracking optical system200A. The recording and reading optical system 100A is an optical systemthat performs recording and reading on/from a first group of recordingand reading layers 14 in the optical recording medium 10. The trackingoptical system 200A is an optical system that performs tracking controlusing first and second servo layers 18 and 20 when information isrecorded in the first group of recording and reading layers 14 using therecording and reading optical system 100A.

A beam 270A from the tracking optical system 200A is converted into aconverging beam by an objective lens 156A and condenses on either of thefirst and the second servo layers 18 and 20 formed inside the opticalrecording medium 10. The beam 270A reflected by the first or secondservo layer 18 or 20 passes through the objective lens 156A and isreflected by a beam splitter 260A, converted into linearly-polarizedlight, which is different by 90 degrees in phase from that on theoutward path, by a quarter-wave plate 254A, and then further reflectedby a polarizing beam splitter 252A.

As illustrated in FIG. 53, when information is recorded in a secondgroup of recording and reading layers 34 by means of a recording andreading optical system 100B in the second optical pickup 90B, a trackingerror (TE) signal obtained as a result of the first or second servolayer 18 or 20 being irradiated by the tracking optical system 200A inthe first optical pickup 90A is used.

Referring back to FIG. 51, an access controller 82 in the trackingcontrol device 80 controls the first and second optical pickups 90A and90B as described below.

(Control performed by access controller during recording) The accesscontroller 82 receives a recording and reading layer that is a recordingtarget, and a tracking number thereof, from the later-described digitalsignal processing device 86, and determines whether the recording andreading layer that is a recording target is one that uses the firstservo layer 18 to perform recording and reading, or one that uses thesecond servo layer 20 to perform recording and reading. Furthermore, theaccess controller 82 applies the tracking beam 270A from the firstoptical pickup 90A to a land/groove corresponding to a tracking numberof the first or second servo layer 18 or 20 obtained as a result of thedetermination. This can be achieved by the access controller 82performing feedback control of actuators 191A and 192A and the firstlinear motion mechanism 75A upon receipt of a tracking error (TE) signalobtained from the beam 270A from the tracking optical system 200A. Inthis state, the first optical pickup 90A applies a recording and readingbeam 170A to the first group of recording and reading layers 14 torecord information thereon.

Simultaneously with this, the access controller 82 controls actuators191B and 192B and the second linear motion mechanism 75B using thetracking error (TE) signal from the first optical pickup 90A. In otherwords, the actuators 191A, 191B and the actuators 192A and 192B, and thefirst linear motion mechanism 75A and the second linear motion mechanism75B operate in a perfectly same manner in the tracking direction. Inthis state, the second optical pickup 90B applies a recording andreading beam 170B to the second group of recording and reading layers 34to record information thereon. As a result, in the present embodiment,the first and second optical pickups 90A and 90B are simultaneouslysubjected to tracking control using the common first or second servolayers 18 or 20 to simultaneously record information on the first andsecond groups of recording and reading layers 14 and 34.

(Control performed by access controller during reproduction)Reproduction from the first group of recording and reading layers 14 isperformed by applying the beam 170A from the recording and readingoptical system 100A in the first optical pickup 90A to the first groupof recording and reading layers 14. Tracking control in this case isperformed by the access controller 82 performing feedback control of theactuators 191A and 192A and the first linear motion mechanism 75Adirectly using a tracking error (TE) signal obtained from the recordingand reading beam 170A, without using the tracking beam 270A.

Reproduction from the second group of recording and reading layers 34 isperformed by applying the beam 170B from the recording and readingoptical system 100B in the second optical pickup 90B to the second groupof recording and reading layers 34. Tracking control in this case isperformed by the access controller 82 performing feedback control of theactuators 191B and 192B and the second linear motion mechanism 75Bdirectly using a tracking error (TE) signal obtained from the recordingand reading beam 170B from the second optical pickup 90B. In otherwords, in the present embodiment, the first and second optical pickups90A and 90B are separately subjected to tracking control, andinformation on the first group of recording and reading layers 14 andinformation on the second group of recording and reading layers 34 aresimultaneously reproduced.

The digital signal processing device 86 includes a reproducing unit 87A,a recording unit 87B, a dividing/synthesizing unit 87C and aninput/output interface unit 87D.

The reproducing unit 87A controls power of light sources 101A and 101Bin the first and second optical pickups 90A and 90B to be constantly apredetermined reproduction level, thereby reproducing informationrecorded on the optical recording medium 10. Furthermore, thereproducing unit 87A receives analog reading signals from the first andsecond optical pickups 90A and 90B, and converts the analog signals intodigital signals.

More specifically, the reproducing unit 87A decodes the analog signalsinto digital signals by means of, e.g., an A/D converter, a PR equalizerand an ML decoder, which are not specifically illustrated. The A/Dconverter converts a reproduced waveform into digital values. The PRequalizer performs sampling of the digital values and performsequalization processing so as to bring voltage levels thereof close to aPR reference class characteristic. The ML decoder selects a maximumideal response from the signals subjected to the equalization processingin the PR equalizer to create binarized digital signals. As a result,the information recorded in the first group of recording and readinglayers 14 is reproduced by the first optical pickup 90A into digitalizedfirst data. Also, the information recorded in the second group ofrecording and reading layers 34 is reproduced by the second opticalpickup 90B into digitalized second data. The first and second data aretransferred to the dividing/synthesizing unit 87C.

The recording unit 87B individually controls power of the light sources101A and 101B in the first and second optical pickups 90A and 90B basedon a predetermined recording strategy, thereby recording/erasinginformation on/from the optical recording medium 10. More specifically,the recording unit 87B controls the recording power of the light source101A in the first optical pickup 90A, thereby recording the first dataon the first group of recording and reading layers 14. Also, therecording unit 87B controls the recording power of the light source 101Bin the second optical pickup 90B, thereby recording the second data onthe second group of recording and reading layers 34. The first data andthe second data are ones received from the dividing/synthesizing unit87C.

The dividing/synthesizing unit 87C divides data to be recorded intofirst data and second data, which have been received from theinput/output interface unit 87D, and conveys the first data and thesecond to the recording unit 87B. The dividing/synthesizing unit 87Ccombines the first data and the second data received from thereproducing unit 87A to form one reproduced data, and conveys thereproduced data to the input/output interface unit 87D.

The input/output interface unit 87D receives/provides an input/output ofinformation from/to an external information appliance. Morespecifically, the input/output interface unit 87D receives data to berecorded, from the external information appliance, and/or outputsreproduced data from the optical recording medium 10 to the externalinformation appliance.

FIG. 54 is an enlarged view of a cross-sectional structure of theoptical recording medium 10 of the present embodiment.

The optical recording medium 10 has a discoid shape with an outerdiameter of approximately 120 mm and a thickness of approximately 1.2mm. The optical recording medium 10 includes a first surface 10A, afirst cover layer 11, the first group of recording and reading layers 14and a first group of intermediate layers 16, a first buffer layer 17,the first servo layer 18, an inter-servo buffer layer 19, the secondservo layer 20, a support substrate 12, a second buffer layer 37, thesecond group of recording and reading layers 34 and a second group ofintermediate layers 36, a second cover layer 31 and a second surface 30Ain this order from the first surface 10A side.

On the first surface 10A side of the support substrate 12, a land 20Aand a groove 20B are provided in spirals. The land 20A and the groove20B form a concavo-convex pattern (groove) for tracking control. Theland 20A and the groove 20B will serve as a future second servo layer20, which is used for tracking control.

In other words, the second servo layer 20 formed on the supportsubstrate 12 includes the concavo-convex pattern (the land 20A and thegroove 20B) for tracking control, which has been formed on a surface ofthe support substrate 12, and a reflective layer formed thereon.

Here, a pitch P1 between adjacent lands 20A or between adjacent grooves20B of the second servo layer 20 is set to be smaller than 0.74 μm. Morespecifically, the pitch P1 is preferably set to be within a range from0.6 to 0.7 μm, and more preferably set to around 0.64 μm. The pitch P1(around 0.64 μm) between adjacent lands 20A or adjacent grooves 20B ofthe second servo layer 20 has a size allowing sufficient tracking to beperformed using the beam 270A in a relatively-long, red wavelengthrange. In the present embodiment, tracking is performed using both theland 20A and the groove 20B. Consequently, a track pitch P2 of recordingmarks is set to be smaller than 0.37 μm relative to the pitch P1 of thesecond servo layer 20, is preferably set to be within a range from 0.26to 0.35 μm, and more preferably set to around 0.32 μm, which is a half(½) of the pitch P1. Consequently, the track pitch P2 between therecording marks is around 0.32 μm, which is compatible with the BDstandards. As described above, tracking control is performed using theland 20A and the groove 20B, respectively, enabling the track pitch P2between the recording marks of the group of recording and reading layers14 to be reduced even though the pitch P1 of the second servo layer 20is not reduced.

The inter-servo buffer layer 19, which is provided on a surface of thesecond servo layer 20, includes a light transmissive, acrylicultraviolet curable resin. A thickness of the inter-servo buffer layer19 is set to, for example, 30 μm. On a surface of the inter-servo bufferlayer 19, a land 18A and a groove 18B are formed in spirals using astamper for a light transmitting resin. The land 18A and the groove 18Bform a concavo-convex pattern (groove) for tracking control in the firstservo layer 18. A direction of the spirals of the land 18A and thegroove 18B are opposite to that of the land 20A and the groove 20B ofthe second servo layer 20.

The first servo layer 18 formed on the inter-servo buffer layer 19includes the concavo-convex pattern for tracking control (the land 18Aand the groove 18B), which have been formed on the surface of theinter-servo buffer layer 19, and a reflective layer formed thereon.Here, a metal film of, e.g., Al or Ag is formed as a reflective layer bysputtering so as to function as a simple light-reflecting film. Thefirst servo layer 18 is set to have a high transmittance compared to thesecond servo layer 20. If a recording film that can record informationin addition to the reflecting function is provided, a film configurationthat is substantially similar to that of recording and reading layers14A to 14F, which will be described later, may be provided.

A pitch P1 between adjacent lands 18A or between adjacent grooves 18B ofthe first servo layer 18 is made to correspond to that of the secondservo layer 20. More specifically, the pitch P1 is set to around 0.64μm.

The first buffer layer 17 includes a light transmissive, acrylicultraviolet curable resin, and a thickness of the first buffer layer 17is set to 208 μm.

With the above-described configuration, a boundary between the supportsubstrate 12 and the first buffer layer 17 (i.e., the second servo layer20) in the optical recording medium 10 is located 350 μm from the firstsurface 10A. Also, the first servo layer 18 is located 320 μm from thefirst surface 10A.

The rest of the structure is the same as that of the optical recordingmedium of the fifth embodiment. Consequently, the optical recordingmedium 10 has a symmetrical structure in a thickness direction exceptasymmetrical arrangement of the first and second servo layers 18 and 20.

Next, a method for producing the optical recording medium 10 of theninth embodiment will be described.

As illustrated in FIG. 55A, a support substrate 12 with a groove and aland formed only on one side thereof is fabricated. Subsequently, aservo layer 20 is formed on a surface of the support substrate 12 on theside where the groove and the land are provided. The servo layer 20 isformed by forming a film having reflectivity for light from the lightsource in the tracking optical system 200A (for example, a metal filmof, e.g., Al or Ag) by means of, e.g., sputtering.

Next, as illustrated in FIG. 55B, an inter-servo buffer layer 19 isformed on the second servo layer 20 side of the support substrate 12where the second servo layer 20 has been formed. Here, a groove 18B anda land 18A are formed on a surface of the inter-servo buffer layer 19.More specifically, two opposite surfaces of the support substrate 12 arecoated with an acrylic or epoxy ultraviolet curable resin with anadjusted viscosity, by means of, e.g., spin coating, and a groove 18Band a land 18A are formed using a transparent resin stamper on theinter-servo buffer layer 19 side of the support substrate 12, and thenirradiated with ultraviolet light and thereby cured. Consequently, theinter-servo buffer layer 19 is formed. An inter-servo buffer layer 19can be formed on the surface of the second servo layer 20 by means of,e.g., spraying or dipping, instead of an ultraviolet curable resin.

Subsequently, a first servo layer 18 is formed on a surface of theinter-servo buffer layer 19. More specifically, a film having bothreflectivity and transmissivity for light from the light source in thetracking optical system 200A (for example, a metal thin film of, e.g.,Al or Ag) is formed on the surface of the inter-servo buffer layer 19 bymeans of, e.g., sputtering.

Next, as illustrated in FIG. 55C, a first buffer layer 17 and a secondbuffer layer 37 are simultaneously formed on a surface of the firstservo layer 18 and a surface 30A on the opposite side of the supportsubstrate 12.

Next, as illustrated in FIG. 55D, an L0 recording and reading layer 14Ain the first group of recording and reading layers 14 and an L0recording and reading layer 34A in the second group of recording andreading layers 34 are simultaneously formed on the first buffer layer 17and the second buffer layer 37, respectively.

Upon completion of formation of an L5 recording and reading layer 14F inthe first group of recording and reading layers 14 and an L5 recordingand reading layer 34F in the second group of recording and readinglayers 34, as illustrated in FIG. 55D, first and second cover layers 11and 31 are simultaneously formed thereon, whereby the optical recordingmedium 10 is completed.

Next, an optical recording and reading method for recording and readinginformation on/from the optical recording medium 10 using the opticalrecording and reading apparatus 70 of the present embodiment will bedescribed with reference to FIGS. 56 to 59. In the present embodiment, astep of recording information simultaneously on the first and secondgroups of recording and reading layers using the first servo layer 18,and a step of recording information simultaneously on the first andsecond groups of recording and reading layers using the second servolayer 20 are alternately repeated.

First, a precondition for executing the optical recording and readingmethod will be described. As illustrated in FIG. 59, the opticalrecording medium 10 is arranged on a spindle S with the first surface10A downside and the second surface 30A upside. Viewed from below thespindle S in an axis direction, the optical recording medium 10 rotatesclockwise. A first spiral direction of the land 18A and the groove 18Bof the first servo layer 18 is set to a direction in which the spiralsspread counterclockwise from the inner peripheral side toward the outerperipheral side when the optical recording medium 10 is viewed from thefirst surface 10A side. Meanwhile, a second spiral direction of the land20A and the groove 20B of the second servo layer 20 is set to adirection that the spirals spread clockwise from the inner peripheralside toward the outer peripheral side when the optical recording medium10 is viewed from the first surface 10A side, that is, a directionopposite to the first spiral direction. Here, recording or readingon/from the first group of recording and reading layers 14 using thefirst optical pickup 90A is referred to as a first recording and readingoperation, and recording or reading on/from the second group ofrecording and reading layers 34 using the second optical pickup 90B isreferred to as a second recording and reading operation.

<Simultaneous Recording of Information in First and Second Groups ofRecording and Reading Layers Using First Servo Layer>

The input/output interface unit 87D in the digital signal processingdevice 86 receives data to be recorded, from the external informationappliance, and transmits the data to the dividing/synthesizing unit 87C.The dividing/synthesizing unit 87C divides the received data to berecorded into first data and second data and conveys the first data andthe second data to the recording unit 87B. The recording unit 87Bcontrols the recording power of the light source 101A in the firstoptical pickup 90A to record the first data on the first group ofrecording and reading layers 14 (first recording and reading operation).Simultaneously with that, the recording unit 87B controls the recordingpower of the light source 101B in the second optical pickup 90B torecord the second data on the second group of recording and readinglayers 34 (second recording and reading operation). Details of the firstand second recording and reading operations will be described below.

(First recording and reading operation) As illustrated in FIGS. 56 and59A, when recording information on the L0 recording and reading layer14A in the first group of recording and reading layers 14, the beam 270Ain the red wavelength range from the tracking optical system 200A in thefirst optical pickup 90A is applied to the first servo layer 18 from thefirst surface 10A to perform tracking. More specifically, a spot of thebeam 270A is applied to the groove 18B and the land 18A of the firstservo layer 18 to perform tracking.

Furthermore, simultaneously with the tracking, the recording beam 170Ain a blue wavelength range from the recording and reading optical system100A in the first optical pickup 90A is applied to the L0 recording andreading layer 14A from the first surface 10A.

As a result, information is recorded on the L0 recording and readinglayer 14A from the inner peripheral side toward the outer peripheralside along the groove 18B and the land 18A relative to the opticalrecording medium 10 that rotates clockwise viewed from the first surface10A side. The track pitch P2 of recording marks formed at the L0recording and reading layer 14A is a half of the pitch P1 betweengrooves 18B or between lands 18A.

(Second recording and reading operation) When recording information onthe L0 recording and reading layer 34A in the second group of recordingand reading layers 34, tracking control of the second optical pickup 90Bis performed using a tracking error signal from the first optical pickup90A in the first recording and reading operation. Consequently, theoptical axes of the first optical pickup 90A and the second opticalpickup 90B face each other and substantially correspond to each other.In this state, a recording beam 170B in a blue wavelength range from therecording and reading optical system 100B in the second optical pickup90B is applied to the L0 recording and reading layer 34A.

As a result, as illustrated in FIG. 59A, information is recorded on theL0 recording and reading layer 34A from the inner peripheral side towardthe outer peripheral side along the groove 18B and the land 18A of thefirst servo layer 18 relative to the optical recording medium 10 thatrotates counterclockwise viewed from the second surface 30A side. Thetrack pitch P2 of recording marks formed at the L0 recording and readinglayer 34A is also a half of the pitch P1 between grooves 18B or betweenlands 18A of the first servo layer 18.

The first recording operation and the second recording operation, whichhave been described above, are concurrently performed, thereby achievingsimultaneous recording of information on the first and second groups ofrecording and reading layers 14 and 34 using the first servo layer 18.

Information on basic specifications of the optical recording medium 10and the number of layers stacked in each of the first and second groupsof recording and reading layers 14 and 34 are previously recorded in arecording pit or a BCA (burst cutting area) of the first servo layer 18.Accordingly, such information is always read by the beam 270A in the redwavelength range before start of tracking control. The basicspecifications of the optical recording medium 10 include positions ofthe first and second servo layers 18 and 20, positions of the respectiverecording and reading layers, and rules on an inter-layer distance inthe groups of recording and reading layers.

After completion of necessary information recording on the L0 recordingand reading layer 14A in the first group of recording and reading layers14 and the L0 recording and reading layer 34A in the second group ofrecording and reading layers 34, relevant additional information (e.g.,address information on recording and content information) issimultaneously recorded in management areas provided in advance in partsof the L0 recording and reading layers 14A and 34A.

Subsequently, when information recording on the L0 recording and readinglayers 14A and 34A is resumed, first, the information in the managementareas of the L0 recording and reading layers 14A and 34A is reproducedto check positions where the previous recording has been completed, andrecording is continued from those positions. As described above,recording is simultaneously continued until completion of informationrecording on all data areas of the L0 recording and reading layers 14Aand 34A.

<Simultaneous Recording of Information in First and Second Groups ofRecording and Reading Layers Using Second Servo Layer>

Upon end of recording on data areas of the L0 recording and readinglayers 14A and 34A, as illustrated in FIGS. 57 and 59B, recording ondata areas of the L1 recording and reading layers 14B and 34B adjacentto the L0 recording and reading layers 14A and 34A is started.

(First recording and reading operation) When recording information onthe L1 recording and reading layer 14B in the first group of recordingand reading layers 14, the beam 270A in the red wavelength range fromthe first optical pickup 90A is applied to the second servo layer 20from the first surface 10A to perform tracking. More specifically, aspot of the beam 270A is applied to the groove 20B and the land 20A ofthe second servo layer 20 to perform tracking.

Furthermore, simultaneously with the tracking, the recording beam 170Ain the blue wavelength range from the recording and reading opticalsystem 100A in the first optical pickup 90A is applied from the firstsurface 10A to the L1 recording and reading layer 14B.

As a result, information is recorded on the L1 recording and readinglayer 14B from the outer peripheral side toward the inner peripheralside along the groove 20B and the land 20A relative to the opticalrecording medium 10 that rotates clockwise (first rotation direction)viewed from the first surface 10A side. A track pitch P2 of recordingmarks formed on the L1 recording and reading layer 14B is a half of thepitch P1 between grooves 20B or between lands 20A.

(Second recording and reading operation) When recording information onthe L1 recording and reading layer 34B in the second group of recordingand reading layers 34, tracking control of the second optical pickup 90Bis performed using a tracking error signal from the first optical pickup90A in the first recording and reading operation. Simultaneously withthe tracking, the recording beam 170B in the blue wavelength range fromthe recording and reading optical system 100B in the second opticalpickup 90B is applied to the L1 recording and reading layer 34B.

As a result, information is recorded on the L1 recording and readinglayer 34B from the outer peripheral side toward the inner peripheralside along the groove 20B and the land 20A of the second servo layer 20relative to the optical recording medium 10 that rotatescounterclockwise (second rotation direction) viewed from the secondsurface 30A side. A track pitch P2 of recording marks formed on the L1recording and reading layer 34B is also a half of the pitch P1 betweengrooves 20B or between lands 20A of the second servo layer 20.

The first recording operation and the second recording operation, whichhave been described above, are concurrently performed, thereby achievingsimultaneous recording of information on the first and second groups ofrecording and reading layers 14 and 34 using the second servo layer 20.

After completion of necessary information recording on the L1 and L2recording and reading layers 14B and 34B, relevant additionalinformation (e.g., address information on the recording and contentinformation) is recorded in the aforementioned management areas of theL0 recording and reading layers 14A and 34A.

As a result of repetition of the above recording operations, in thepresent optical recording and reading method, as indicated by arrow Q inFIG. 57, recording from the inside toward the outside in a radialdirection of the optical recording medium 10 using the first servo layer18 and recording from the outside toward the inside in the radialdirection of the optical recording medium 10 using the second servolayer 20 are alternately performed.

Furthermore, in the present embodiment, information is recordedsimultaneously on a pair of recording and reading layers in a sameordinal position from the center side in the thickness direction in thefirst and second groups of recording and reading layers 14 and 34.Specifically, a pair of recording and reading layers is selected instacking order from the center side toward the outside in the thicknessdirection of the optical recording medium 10, and information isrecorded on the pair of recording and reading layers.

Here, although a case where management areas are provided in the L0recording and reading layers 14A and 34A has been described, managementareas can be provided in other recording and reading layers. Also, wherethe first and second servo layers 18 and 20 have recording films, it ispreferable that management areas be provided in the first and secondservo layers 18 and 20 to record additional information therein.Recording on the first and second servo layers 18 and 20 may beperformed using the beam 270A used for tracking control. Concentrationof management information in the first and second servo layers 18 and 20enables simultaneous obtainment of management information on both thefirst group of recording and reading layers 14 and the second group ofrecording and reading layers 34.

<Simultaneous Reproducing of Information from First and Second Groups ofRecording and Reading Layers>

When the digital signal processing device 86 receives a request forreproducing data recorded on the optical recording medium 10, from theexternal information appliance, the reproducing unit 87A in the digitalsignal processing device 86 controls the power of the light sources 101Aand 101B in the first and second optical pickups 90A and 90B to beconstantly a predetermined reproduction level, thereby reproducing theinformation recorded on the optical recording medium 10. As alreadydescribed in the recording operations, in the present embodiment, datato be recorded is divided into first data and second data, which arethen separately recorded in paired recording and reading layers in asame ordinal position in the first and second groups of recording andreading layers 14 and 34. Thus, during reproduction, the first data andthe second data are simultaneously reproduced and combined toreconstruct reproduced data.

(First recording and reading operation) As illustrated in FIG. 58, whenthe first data recorded on the L0 recording and reading layer 14A in thefirst group of recording and reading layers 14 is reproduced, thereproduction is performed while the beam 170A from the recording andreading optical system 100A in the first optical pickup 90A is appliedto the L0 recording and reading layer 14A to perform tracking controland focus control.

(Second recording and reading operation) When the second data recordedon the L0 recording and reading layer 34A in the second group ofrecording and reading layers 34 is reproduced, the reproduction isperformed while the beam 170B from the recording and reading opticalsystem 100B in the second optical pickup 90B is applied to the L0recording and reading layer 34A to perform tracking control and focuscontrol.

The first reproducing operation and the second reproducing operation areconcurrently performed, thereby achieving simultaneous reproducing ofthe first data and the second data on the first and second groups ofrecording and reading layers 14 and 34. Although tracking control isperformed using the first and second servo layers 18 and 20 duringrecording, during simultaneous reproducing, the first and second opticalpickups 90A and 90B are separately and respectively subjected totracking control using the recording and reading optical systems 100Aand 100B.

The reproducing unit 87A receives analog reading signals from the firstand second optical pickups 90A and 90B, and converts the analog signalsinto digital signals, thereby obtaining the first data and the seconddata. Furthermore, the reproducing unit 87A transfers the first andsecond data to the dividing/synthesizing unit 87C. Thedividing/synthesizing unit 87C combines the first and second datareceived from the reproducing unit 87A to form one reproduced data, andconveys the reproduced data to the input/output interface unit 87D. Theinput/output interface unit 87D outputs the reproduced data to theexternal information appliance.

As described above, according to the optical recording and readingmethod of the ninth embodiment, while tracking control is performed byapplying the tracking beam 270A to the first or second servo layer 18 or20, the recording and reading beam 170A is applied to the first group ofrecording and reading layers 14 that rotates clockwise viewed from thefirst surface 10A side, thereby recording or reading information, andsimultaneously with that, the recording and reading beam 170B is appliedto the second group of recording and reading layers 34 that rotatescounterclockwise viewed from the second surface 30A side, therebyrecording or reading information. Consequently, information can berecorded or reproduced on or from a pair of recording and reading layerssimultaneously, enabling a substantial increase in information transferrate.

Furthermore, in the optical recording and reading method, either of thefirst and second servo layers 18 and 20 is shared to simultaneouslyrecord information on a pair of recording and reading layers while anoptical axis of the recording and reading beam 170A from the firstoptical pickup 90A and an optical axis of the recording and reading beam170B from the second optical pickup 90B are maintained to substantiallycorrespond to each other. As a result, the first data and the seconddata are always recorded in a same tracking position, enablingsimplification of reproducing control for simultaneous reproducing.Furthermore, in the second optical pickup 90B in the optical recordingand reading apparatus 70, a tracking optical system can be omitted,enabling simplification of the structure.

In the present embodiment, if a large amount of the tracking beam 270Aapplied to the second servo layer 20 passes through the second servolayer 20, such large amount of the tracking beam 270A may adverselyaffect the second optical pickup 90B arranged on the same axis.Therefore, in the optical recording medium 10, a transmittance for thetracking beam 270A of the second servo layer 20 is set to no greaterthan 10%, thereby suppressing the adverse effect of the beam 270A on thesecond optical pickup 90B side.

Also, the digital signal processing device 86 in the optical recordingand reading apparatus 70 divides data to be recorded, which has beenreceived from the external information appliance, into first data forfirst recording operation and second data for second recording operationto simultaneously record the first data and the second data on pairedrecording and reading layers. Furthermore, the digital signal processingdevice 86 simultaneously reproduces the first data and the second datarecorded simultaneously on the paired recording and reading layers, andcombines the first data and the second data to output the combined datato the external information appliance as if the combined data is onereproduced data. Accordingly, an interface that is the same as those ofconventional optical recording and reading apparatuses that performrecording or reading on or from one recording and reading layer can beprovided for the external information appliance, and thus, the need tochange specifications of the external information appliance can beeliminated.

Furthermore, in the present optical recording and reading method, theoptical recording medium 10 includes the first servo layer 18 thatincludes a concavo-convex pattern or a groove for tracking control,which extend in the first spiral direction, and a second servo layer 20including a concavo-convex pattern or a groove for tracking control,which extend in the second spiral direction opposite to the first spiraldirection, as servo layers. Furthermore, a step of performing the firstrecording operation and the second recording operation simultaneouslywhile the first servo layer 18 is shared to perform tracking control ofthe optical recording medium 10 from the inner peripheral side towardthe outer peripheral side and a step of performing the first recordingoperation and the second recording operation simultaneously while thesecond servo layer 20 is shared to perform tracking control of theoptical recording medium 10 from the outer peripheral side toward theinner peripheral side are alternately switched from each other everytime the recording and reading layer is switched from one another.Accordingly, as illustrated in FIG. 57, when the recording and readinglayer is switched to another, merely moving the recording and readingbeams 170A and 170B from the first and second optical pickups 90A and90B in a focus direction enables the recording and reading beams 170Aand 170B to be quickly moved to a recording start position or areproducing start position in a pair of recording and reading layers,which are destinations of the movement. Consequently, a decrease intransfer rate at the time of switching of recording and reading layerscan be suppressed.

Furthermore, in the present optical recording and reading method, awavelength of the tracking beam 270A and a wavelength of the recordingand reading beams 170A and 170B are set to be different from each other.Specifically, the wavelength of the tracking beam 270A is set to 630 to680 nm in the red wavelength range, and the wavelength of the recordingand reading beams 170A and 170B are set to 380 to 450 nm in the bluewavelength range.

In addition, in the optical recording medium 10, a reflectance of thefirst and second servo layers 18 and 20 when the tracking beam 270A inthe red wavelength range is applied thereto is set to be larger comparedto a reflectance assuming that the recording and reading beam 170A isapplied to the first and second servo layers 18 and 20. Morespecifically, in order to provide such reflectance, a material thatabsorbs a larger amount of light as the wavelength of the beam isshorter is selected for the first buffer layer 17.

Consequently, even if the recording and reading beam 170A having awavelength in the blue wavelength range is incident on the first andsecond servo layers 18 and 20, such recording and reading beam 170A iseasily absorbed by the first buffer layer 17, enabling suppression of anamount of light reaching the first and second servo layers 18 and 20(amount of reflected light from the first and second servo layers 18 and20). Meanwhile, the tracking beam 270A from the first optical pickup 90Acan actively pass through the first buffer layer 17, and thus, theamount of light reaching the first and second servo layers 18 and 20(amount of reflected light from the first and second servo layers 18 and20) can be increased. Consequently, stable tracking control can beprovided while the quality of reading signal is increased.

While in the present embodiment, the first buffer layer 17 is providedwith a characteristic exhibiting different absorptivities for a trackingbeam (red wavelength) and a recording and reading beam (bluewavelength), and the first and second servo layers 18 and 20consequently have different reflectances for the tracking beam and therecording and reading beam, the present invention is not limited to thiscase. For example, the reflecting films formed on the first and secondservo layers 18 and 20 themselves may be provided with wavelengthdependence so as to exhibit different reflectances for differentwavelengths. Also, separately from the first buffer layer 17, a filterlayer having wavelength dependence for light transmittance and/orabsorptance may be formed.

Furthermore, in the optical recording and reading method, information isrecorded simultaneously on recording and reading layers in a sameordinal position in the first group of recording and reading layers 14and the second group of recording and reading layers 34, from a centerin the thickness direction of the optical recording medium 10.Consequently, the paired recording and reading layers that are recordingtargets are similar to each other in their distances from the respectivesurfaces 10A and 30A of the optical recording medium 10, and the beamshave optical paths symmetrical to each other. Consequently, for example,a control signal obtained in the first optical pickup 90A, morespecifically, control information such as inclination or wobbling of theoptical recording medium 10 can be used as it is for a control signalfor the second optical pickup 90B by reversing the polarity of suchinformation. Consequently, in the second optical pickup 90B, a specialphotodiode mechanism or the like for obtaining such control signal canbe omitted.

Furthermore, in the optical recording medium 10, the first buffer layer17 and the second buffer layer 37, which are relatively thick, are madeto have thicknesses similar to each other, and the first and secondbuffer layers 17 and 37 are simultaneously formed, enabling suppressionof warpage of the support substrate 12.

This means that the support substrate 12 can be made to be thin and canalso be made to include a material having a low rigidity, and thus, thespaces for forming recording and reading layers can be accordinglyincreased.

In particular, in the present embodiment, when producing the opticalrecording medium 10, except the inter-servo buffer layer 19, the firstbuffer layer 17 and the second buffer layer 37, the first group ofrecording and reading layers 14 and the second group of recording andreading layers 34, and the first group of intermediate layers 16 and thesecond group of intermediate layers 36 are simultaneously formed onsurfaces on the opposite sides. Consequently, internal stress generatedduring ultraviolet curing is equally imposed on the opposite sides ofthe support substrate 12, enabling further reduction of warpage of theoptical recording medium 10.

While the optical recording and reading method of the above-describedembodiment has been described in terms of a case where information isrecorded on the layers in the first and second groups of recording andreading layers 14 and 34 in stacking order from the center side towardthe outside in the thickness direction of the optical recording medium10, the present invention is not limited to this case.

For example, information can be recorded on layers in the first andsecond groups of recording and reading layers 14 and 34 in layer orderfrom the outside toward the center side of the optical recording medium10. Also, a pair of recording and reading layers in a same ordinalposition is randomly extracted from the first and second groups ofrecording and reading layers 14 and 34 to perform recording thereon.

Furthermore, although the optical recording and reading method of theabove-described embodiment has been described in terms of a case whereinformation is recorded or reproduced on or from a pair of recording andreading layers in a same ordinal position from the center side in thethickness direction of the optical recording medium 10, the presentinvention is not limited to this case. For example, as indicated byarrow Q in FIG. 60, a pair of recording and reading layers can beselected from the first and second groups of the recording and readinglayers 14, 34 such that the ordinal position of the recording andreading layer of the first group in order from the first surface 10Aside for the first recording and reading operation corresponds to theordinal position of the recording and reading layer of the second groupin order from the center side in the thickness direction of the opticalrecording medium 10 for the second recording and reading operation

Consequently, an interfocal distance T between a focal point of therecording and reading beam 170A on the first optical pickup 90A side anda focal point of the recording and reading beam 170B on the secondoptical pickup 90B side can be made to be constant or relatively stable.As a result, the number of intermediate layers 16 and 36 that arepresent between the focal points of the paired beams 170A and 170B aremade to be always constant. Accordingly, an amount of change in theinterfocal distance T due to errors in film formation of the groups ofintermediate layers 16 and 36 can be kept within a fixed range, whichleads to reduction in, e.g., focus errors. In particular, when the beams170A and 170B jump on next recording and reading layers, also, theprobability of the beams 170A and 170B jumping to wrong recording andreading layers can be reduced if the focal points of the beams 170A and170B are simultaneously moved with the interfocal distance T fixed.

Furthermore, although the optical recording medium 10 of theabove-described embodiment has been described in terms of a case wherethe first cover layer 11 and the second cover layer 31 are made to havea same thickness, the present invention is not limited to this case. Forexample, like the optical recording medium 10 illustrated in FIG. 61, itis preferable that the first cover layer 11 and the second cover layer31 be made to have different thicknesses. More specifically, thethickness of the first cover layer 11 is set to be larger by the amountof the thickness of the support substrate 12, compared to the thicknessof the second cover layer 31. Consequently, the first and second servolayers 18 and 20 are positioned at the center in the thickness directionof the optical recording medium 10. Also, when producing the opticalrecording medium 10, it is preferable to separately stack a first coverlayer 11 and a second cover layer 31 having different thicknesses. Eventhough these layers are not simultaneously stacked, a certain level ofrigidity has already been provided by the support substrate 12, thefirst and second buffer layers 17 and 37, the first group of recordingand reading layers 14 and the first group of intermediate layers 16, andthe second group of recording and reading layers 34 and the second groupof intermediate layers 36, and thus, warpage and/or deformation of theoptical recording medium 10 are sufficiently suppressed.

Also, like the optical recording medium 10 illustrated in FIG. 62,thicknesses of the first and second buffer layers 17 and 37 or theinter-layer distance or the number of layers in the first and secondgroups of recording and reading layers 14 and 34 can be made to bedifferent from each other to consequently position the first and secondservo layers 18 and 20 at the center in the thickness direction.

Furthermore, although the above embodiment has been described only interms of a case where recording layers have already been formed inadvance as recording and reading layers in the first and second groupsof recording and reading layers 14 and 34, the present invention is notlimited to this case. For example, like the optical recording medium 10illustrated in FIG. 63, first and second bulk layers 13 and 33 havingpredetermined thicknesses can be formed in entire areas in which futurefirst and second groups of recording and reading layers may be formed.Upon application of the recording beams 170A and 170B to the first andsecond bulk layers 13 and 33, only the focal point parts of beam spotschange in state, thereby recording marks being formed. In other words,an optical recording medium according to the present invention is notlimited to those including recording and reading layers formed inadvance, to which beams are applied, and includes an example in whichrecording marks are formed in planar areas as needed, and as aggregatesof the recording marks, the first and second groups of recording andreading layers 14 and 34 are formed ex post facto in multiple layers.Employment of the structures of the bulk layers 13 and 33 in the opticalrecording medium 10 enables positions of recording and reading layers tobe freely set within the areas of the bulk layers 13 and 33. Forexample, even though the first bulk layer 13 and the second bulk layer33 have different thicknesses or are arranged at different positions,distances of the first and second groups of recording and reading layers14 and 34 from the first and second surfaces 10A and 30A can be made tocorrespond to each other. Here, a structure in which cover layers andbuffer layers are omitted when the first and second bulk layers 13 and33 are employed is illustrated.

Also, although the optical recording medium 10 to which the opticalrecording and reading method according to the present embodiment isapplied has been described in terms of a case where both the first andsecond servo layers 18 and 20 are formed on one side of the supportsubstrate 12 and the first group of recording and reading layers 14 andthe second group of recording and reading layers 34 are arranged onopposite surfaces of the support substrate 12, the present invention isnot limited to this case. For example, as illustrated in FIG. 64, it ispossible to arrange the first servo layer 18 on one side of the supportsubstrate 12 and the second servo layer 20 on another side of thesupport substrate 12. The symmetry in the thickness direction of theoptical recording medium 10 is further enhanced, enabling reduction ofwarpage.

INDUSTRIAL APPLICABILITY

The optical recording medium and the optical recording and readingmethod according to the present invention are applicable to varioustypes of optical recording medium having servo layers and recording andreading layers.

The entire disclosure of Japanese Patent Applications No. 2011-22478filed on Feb. 4, 2011, 2011-073934 filed on Mar. 30, 2011, 2011-073929filed on Mar. 30, 2011, 2011-073931 filed on Mar. 30, 2011, 2011-073930filed on Mar. 30, 2011, 2011-073932 filed on Mar. 30, 2011 and2011-073933 filed on Mar. 30, 2011 including specifications, claims,drawings, and summaries are incorporated herein by reference in itsentirety.

1. An optical recording and reading method for recording information ina recording and reading layer in an optical recording medium, theoptical recording medium comprising the recording and reading layer anda servo layer, the recording and reading layer being previously stackedor formed afterward and having no concavo-convex pattern for trackingcontrol, the servo layer having a concavo-convex pattern or a groove fortracking control formed therein, wherein information is recorded in therecording and reading layer while tracking is performed using the servolayer.
 2. The optical recording and reading method according to claim 1,wherein the optical recording medium has a plurality of the recordingand reading layers, the method comprising: a servo layer using step ofrecording information in one of the recording and reading layers whileperforming tracking using the servo layer; and a recorded area usingstep of recording information in another one of the recording andreading layers while performing tracking using information recorded areain the one of the recording and reading layers.
 3. The optical recordingand reading method according to claim 2, wherein in the recorded areausing step, the information is recorded in another one of the recordingand reading layers that is adjacent to the one of the recording andreading layers providing the information recorded area.
 4. The opticalrecording and reading method according to claim 2, wherein in the servolayer using step, the information is recorded in one of the recordingand reading layers that is adjacent to the servo layer.
 5. The opticalrecording and reading method according to claim 2, wherein in the servolayer using step, recording operation is continued until recording ofthe information on all of data area in the one of the recording andreading layers is completed, and wherein in the recorded area usingstep, the information is recorded in the another one of the recordingand reading layers using the recorded area of the one of the recordingand reading layers in the servo layer using step.
 6. The opticalrecording and reading method according to claim 5, wherein in the servolayer using step, recording operation is continued until recording ofthe information on all of data area in the another one of the recordingand reading layers is completed, and then, information is recorded in anext one of the recording and reading layers using the recorded area ofthe another one of the recording and reading layers.
 7. The opticalrecording and reading method according to claim 2, wherein in the servolayer using step, a wavelength of a tracking beam applied to the servolayer is substantially equal to a wavelength of a recording beam appliedto the recording and reading layers, and wherein the servo layer has arecording and reading film able to record information thereon by thetracking beam or the recording beam.
 8. The optical recording andreading method according to claim 1, wherein in the optical recordingmedium, a buffer layer is arranged between the servo layer and one ofthe recording and reading layers that is closest to the servo layer, aplurality of intermediate layers are arranged between the plurality ofrecording and reading layers, and a thickness of the buffer layer issubstantially equal to a thickness of one of the plurality ofintermediate layers.
 9. The optical recording and reading methodaccording to claim 8, wherein in the optical recording medium, thenumber of kinds of thicknesses of the plurality of intermediate layersis set to two or less.
 10. The optical recording and reading methodaccording to claim 1, wherein in the optical recording medium, the servolayer is arranged in a position that is farther from a light incidentsurface than the plurality of the recording and reading layers are. 11.The optical recording and reading method according to claim 1, whereinin the optical recording medium, the servo layer is arranged in aposition that is closer to a light incident surface than the pluralityof the recording and reading layers are.
 12. The optical recording andreading method according to claim 1, wherein a recording and readingbeam having a second wavelength shorter than a first wavelength isapplied to the recording and reading layer to record or read informationwhile a tracking beam having the first wavelength is applied to theservo layer to perform tracking control, and wherein a reflectance ofthe servo layer at a time when light of the recording and reading beamhaving the second wavelength is applied through the recording andreading layer to the servo layer is lower than a reflectance of theservo layer at a time when light of the tracking beam having the firstwavelength is applied through the recording and reading layer to theservo layer.
 13. The optical recording and reading method according toclaim 12, wherein an amount of reflected light from the servo layer at atime when the recording and reading beam is applied through therecording and reading layer to the servo layer is less than or equal tofive times of an amount of reflected light from the recording andreading layer at a time when the recording and reading beam is appliedto the recording and reading layer.
 14. The optical recording andreading method according to claim 13, wherein an amount of reflectedlight from the servo layer at a time when the recording and reading beamis applied through the recording and reading layer to the servo layer isless than an amount of reflected light from the recording and readinglayer at a time when the recording and reading beam is applied to therecording and reading layer.
 15. The optical recording and readingmethod according to claim 12, wherein an inter-layer distance betweenthe recording and reading layer and the servo layer is 10 to 200 μm. 16.The optical recording and reading method according to claim 12, whereinthe reflectance of the servo layer at a time when the tracking beam isapplied through the recording and reading layer to the servo layer is40% to 95%, and the reflectance of the servo layer at a time when therecording and reading beam is applied through the recording and readinglayer to the servo layer by way of experiment is less than or equal to60%.
 17. The optical recording and reading method according to claim 12,wherein the servo layer has a reflecting film that contains metal as amajor component, and an auxiliary film that is arranged adjacent to thereflecting film and is different in reflectance from the reflectingfilm.
 18. The optical recording and reading method according to claim17, wherein the servo layer has the reflecting films the number of whichis two or more, and the auxiliary films the number of which is three ormore.
 19. The optical recording and reading method according to claim12, wherein a filter layer in which dye is bound or dispersed isprovided between the servo layer and the recording and reading layer,and wherein the filter layer has a low absorbance for the firstwavelength of the tracking beam, and a high absorbance for the secondwavelength of the recording and reading beam.
 20. The optical recordingand reading method according to claim 12, wherein a first recording andreading layer is arranged on one side of the servo layer, wherein asecond recording and reading layer is arranged on a side opposite to thefirst recording and reading layer with respect to the servo layer, andwherein information is recorded in the second recording and readinglayer while tracking control is performed using the servo layer.
 21. Theoptical recording and reading method according to claim 20, wherein theservo layer is formed directly on a side of the first recording andreading layer with respect to a substrate, and wherein the secondrecording and reading layer is formed on a side opposite to the servolayer with respect to the substrate.
 22. The optical recording andreading method according to claim 21, wherein the substrate is made of alight transmitting material.
 23. The optical recording and readingmethod according to claim 20, wherein the first recording and readinglayer and the second recording and reading layer are previously stackedor formed afterward in symmetrical positions with respect to a center ofa thickness of the substrate.
 24. The optical recording and readingmethod according to claim 20, wherein the thickness of the substrate is10 to 600 μm.
 25. The optical recording and reading method according toclaim 1, wherein the optical recording medium has a first set of aplurality of the recording and reading layers arranged on a side of afirst surface, and a second set of a plurality of the recording andreading layers arranged on a side of a second surface opposite to thefirst surface, wherein the number of layers of the second set of therecording and reading layers is equal to the number of layers of thefirst set of the recording and reading layers, and wherein a firstrecording and reading operation for recording or reading information byapplying a first recording and reading beam through the first surface tothe first set of the recording and reading layers and a second recordingand reading operation for recording or reading information by applying asecond recording and reading beam through the second surface to thesecond set of the recording and reading layers are performedsimultaneously.
 26. The optical recording and reading method accordingto claim 25, wherein ordinal positions of the first set of the recordingand reading layers during the first recording and reading operation andordinal positions of the second set of the recording and reading layersduring the second recording and reading operation correspond to eachother, wherein the ordinal positions of the first set of the recordingand reading layers are in order from closest to the side of the firstsurface, and the ordinal positions of the second set of the recordingand reading layers are in order from closest to a center of a thicknessof the optical recording medium.
 27. The optical recording and readingmethod according to claim 26, wherein recording or reading is performedon the first set of the plurality of the recording and reading layers inorder from closest to the first surface, and recording or reading isperformed on the second set of the plurality of the recording andreading layers in order from closest to the center of the thickness ofthe optical recording medium.
 28. The optical recording and readingmethod according to claim 26, wherein recording or reading is performedsimultaneously in or from recording and reading layers of the first setand the second set such that the recording and reading layers of thefirst set and the second set are in a same ordinal position in orderfrom closest to the center of the thickness of the recording and readinglayers.
 29. The optical recording and reading method according to claim25, wherein tracking control is performed using the tracking beam andthe servo layer in the first recording and reading operation and thesecond recording and reading operation, wherein the tracking beam andthe servo layer are common in the first and second recording and readingoperations.
 30. The optical recording and reading method according toclaim 25, wherein the servo layer is formed on at least one face of asubstrate of the optical recording medium, and wherein the substrate issubstantially transparent.
 31. The optical recording and reading methodaccording to claim 25, wherein when information is recordedsimultaneously in the first set and the second set of the recording andreading layers by the first recording and reading operation and thesecond recording and reading operation, trial writing is performed bythe first or second recording and reading beam on a trial writing areaof either the first set or the second set of the recording and readinglayers, to set optimum recording powers for both the first and secondrecording and reading beams.
 32. The optical recording and readingmethod according to claim 31, wherein when recording is performedsimultaneously in recording and reading layers of the first set and thesecond set such that the recording and reading layers of the first setand the second set are in even number-th ordinal positions in order fromclosest to a center of a thickness of the optical recording medium,trial writing is performed by the first recording and reading beam on atrial writing area of the first set of the recording and reading layers,to set optimum recording powers for both the first and second recordingand reading beams, and wherein when recording is performedsimultaneously in recording and reading layers of the first set and thesecond set such that the recording and reading layers of the first setand the second set are in odd number-th ordinal positions in order fromclosest to the center of the thickness of the optical recording medium,trial writing is performed by the second recording and reading beam on atrial writing area of the second set of the recording and readinglayers, to set optimum recording powers for both the first and secondrecording and reading beams.
 33. The optical recording and readingmethod according to claim 25, wherein when an optimum recording power ofthe first recording and reading beam for recording in an n-th recordingand reading layer of the first set of the recording and reading layersin order from closest to the center of the thickness of the opticalrecording medium has been undetermined and is to be set, if an optimumrecording power of the second recording and reading beam for recordingin an n-th recording and reading layer of the second set of therecording and reading layers in order from closest to the center of thethickness of the optical recording medium has already been determined,the optimum recording power of the second recording and reading beam isdetermined to be the optimum recording power of the first recording andreading beam, and if the optimum recording power of the second recordingand reading beam for recording in the n-th recording and reading layerof the second set of the recording and reading layers has beenundetermined, trial writing is performed by the first recording andreading beam on a trial writing area of the n-th recording and readinglayer of the first set of the recording and reading layers, to determinethe optimum recording power of the first recording and reading beam, andwherein when an optimum recording power of the second recording andreading beam for recording in an m-th recording and reading layer of thesecond set of the recording and reading layers in order from closest tothe center of the thickness of the optical recording medium has beenundetermined and is to be set, if an optimum recording power of thefirst recording and reading beam for recording in an m-th recording andreading layer of the first set of the recording and reading layers inorder from closest to the center of the thickness of the opticalrecording medium has already been determined, the optimum recordingpower of the first recording and reading beam is determined to be theoptimum recording power of the second recording and reading beam, and ifthe optimum recording power of the first recording and reading beam forrecording in the m-th recording and reading layer of the first set ofthe recording and reading layers has been undetermined, trial writing isperformed by the second recording and reading beam on a trial writingarea of the m-th recording and reading layer of the second set of therecording and reading layers, to determine the optimum recording powerof the second recording and reading beam.
 34. The optical recording andreading method according to claim 25, wherein the first set of therecording and reading layers and the second set of the recording andreading layers are arranged in symmetrical positions with respect to thecenter of the thickness of the optical recording medium.
 35. The opticalrecording and reading method according to claim 1, wherein the opticalrecording medium has a substrate, the servo layer is formed on one faceof the substrate, a first recording and reading layer is arranged on aside of the servo layer of the substrate, and a second recording andreading layer is arranged on a side opposite to the servo layer of thesubstrate, and information is recorded in the first recording andreading layer and the second recording and reading layer while trackingcontrol is performed using the servo layer.
 36. The optical recordingand reading method according to claim 35, wherein the substrate is madeof a light transmitting material.
 37. The optical recording and readingmethod according to claim 35, wherein a first buffer layer is stackedbetween the first recording and reading layer that has been previouslystacked and the servo layer, and a second buffer layer is stackedbetween the second recording and reading layer that has been previouslystacked and the substrate, wherein a thickness of the first buffer layerand a thickness of the second buffer layer are substantially equal toeach other.
 38. The optical recording and reading method according toclaim 37, wherein at a wavelength of a tracking beam applied to theservo layer, a refractive index of the substrate is higher than arefractive index of the second buffer layer.
 39. The optical recordingand reading method according to claim 37, wherein at a wavelength of atracking beam applied to the servo layer, a refractive index of thesubstrate is higher than a refractive index of the first buffer layer.40. The optical recording and reading method according to claim 36,wherein the first recording and reading layer and the second recordingand reading layer are previously stacked or formed afterward insymmetrical positions with respect to a center of a thickness of thesubstrate.
 41. The optical recording and reading method according toclaim 36, wherein the first recording and reading layer comprises aplurality of the recording and reading layers, and the second recordingand reading layer comprises a plurality of the recording and readinglayers.
 42. The optical recording and reading method according to claim36, wherein a first cover layer is stacked outside a recording andreading layer of the first recording and reading layer that is farthestfrom the substrate, and a second cover layer is stacked outside arecording and reading layer of the second recording and reading layerthat is farthest from the substrate, and wherein a thickness of thefirst cover layer is set to be larger by a thickness of the substratethan a thickness of the second cover layer.
 43. The optical recordingand reading method according to claim 36, wherein a tracking beamapplied to the servo layer is set to be longer in wavelength than arecording and reading beam applied to the first or the second recordingand reading layer, and wherein a reflectance of the servo layer in acase where the tracking beam is applied is greater than a reflectance ofthe servo layer in a case where the recording and reading beam isapplied to the servo layer by way of experiment.
 44. The opticalrecording and reading method according to claim 36, wherein a thicknessof the substrate is 10 to 600 μm.
 45. The optical recording and readingmethod according to claim 1, comprising: a first recording operation forrecording information by applying a first recording and reading beam toa first recording and reading layer while performing tracking control byapplying a tracking beam to the servo layer; and a second recordingoperation for recording information by applying a second recording andreading beam to a second recording and reading layer while performingtracking control using the tracking beam and the servo layer that arecommon with the first recording operation.
 46. The optical recording andreading method according to claim 45, wherein the first recording andreading beam in the first recording operation is incident from a firstsurface of the optical recording medium, and wherein the secondrecording and reading beam in the second recording operation is incidentfrom a second surface opposite to the first surface of the opticalrecording medium.
 47. The optical recording and reading method accordingto claim 45, wherein the first recording operation and the secondrecording operation are simultaneously performed to record informationsimultaneously in the first and the second recording and reading layers.48. The optical recording and reading method according to claim 45,wherein in the first recording operation, recording is performed in thefirst recording and reading layer that is arranged on one side withrespect to a center of a thickness of the optical recording medium, andwherein in the second recording operation, recording is performed in thesecond recording and reading layer that is arranged on an opposite sidewith respect to the center of the thickness of the optical recordingmedium.
 49. The optical recording and reading method according to claim48, wherein the first recording and reading layer and the secondrecording and reading layer are arranged in symmetrical positions withrespect to the center of the thickness of the optical recording medium.50. The optical recording and reading method according to claim 45,wherein a transmittance of the tracking beam through the servo layer ofthe optical recording medium is set to be less than or equal to 10%. 51.The optical recording and reading method according to claim 1, wherein afirst recording and reading layer is arranged on a side of a firstsurface of the optical recording medium with respect to the servo layer,and a second recording and reading layer is arranged on a side of asecond surface of the optical recording medium with respect to the servolayer, the method comprising: a first recording operation for recordinginformation in a first rotation direction as viewed from the firstsurface by applying a first recording and reading beam through the firstsurface to the first recording and reading layer while performingtracking control by applying a tracking beam to the servo layer; and asecond recording operation for recording operation in a second rotationdirection opposite to the first rotation direction as viewed from thesecond surface by applying a second recording and reading beam throughthe second surface to the second recording and reading layer whileperforming tracking control using the servo layer that is common withthe first recording operation, wherein the second recording operation isperformed simultaneously with the first recording operation.
 52. Theoptical recording and reading method according to claim 51, wherein thefirst recording operation and the second recording operation aresimultaneously performed while keeping the first recording and readingbeam and the second recording and reading beam to be substantiallycoaxial with each other.
 53. The optical recording and reading methodaccording to claim 51, wherein the first recording operation and thesecond recording operation are simultaneously performed by applying thetracking beam to the servo layer wherein the tracking beam is common inthe first recording operation and the second recording operation. 54.The optical recording and reading method according to claim 51, whereindata to be recorded in the optical recording medium is divided by adigital signal processor that controls the first and second recordingand reading beams, into first data on a side of the first recordingoperation and second data on a side of the second recording operation.55. The optical recording and reading method according to claim 51,wherein the optical recording medium has, as the servo layer, a firstservo layer having a concavo-convex pattern or a groove for the trackingcontrol in a first spiral direction and a second servo layer having aconcavo-convex pattern or a groove for the tracking control in a secondspiral direction opposite to the first spiral direction, the methodcomprising: a step of performing the first recording operation and thesecond recording operation while performing tracking control from aninner periphery side of the optical recording medium toward an outerperiphery side of the optical recording medium using the first servolayer, wherein the first servo layer is common in the first recordingoperation and the second recording operation; and a step of performingthe first recording operation and the second recording operation whileperforming tracking control from the outer periphery side of the opticalrecording medium toward the inner periphery side of the opticalrecording medium using the second servo layer, wherein the second servolayer is common in the first recording operation and the secondrecording operation.
 56. The optical recording and reading methodaccording to claim 51, wherein a wavelength of the tracking beam and awavelength of the first or second recording and reading beam aredifferent from each other.
 57. The optical recording and reading methodaccording to claim 51, wherein a wavelength of the first or secondrecording and reading beam is in a range of 380 to 450 nm.
 58. Anoptical recording and reading apparatus that records information in arecording and reading layer in an optical recording medium, the opticalrecording medium comprising the recording and reading layer and a servolayer, the recording and reading layer being previously stacked orformed afterward and having no concavo-convex pattern for trackingcontrol, the servo layer having a concavo-convex pattern or a groove fortracking control formed therein, wherein the optical recording andreading apparatus records information in the recording and reading layerwhile performing tracking using the servo layer.
 59. The opticalrecording and reading apparatus according to claim 58, wherein theoptical recording medium has a first set of a plurality of the recordingand reading layers on a side of a first surface, and a second set of aplurality of the recording and reading layers on a side of a secondsurface opposite to the first surface, wherein the number of layers ofthe second set of the recording and reading layers is equal to thenumber of layers of the first set of the recording and reading layers,the optical recording and reading apparatus comprising: a firstrecording and reading optical system that is arranged on the side of thefirst surface of the optical recording medium, and that records or readsinformation by applying a first recording and reading beam through thefirst surface to the first set of the recording and reading layers; anda second recording and reading optical system that is arranged on theside of the second surface of the optical recording medium, and thatrecords or reads information by applying a second recording and readingbeam through the second surface to the second set of the recording andreading layers.
 60. The optical recording and reading apparatusaccording to claim 59, wherein the first recording and reading opticalsystem and the second recording and reading optical systemsimultaneously perform recording or reading in or from recording andreading layers of the first set and the second set such that therecording and reading layers of the first set and the second set are ina same ordinal position in order from closest to a center of a thicknessof the optical recording medium.
 61. The optical recording and readingapparatus according to claim 59, wherein ordinal positions of the firstset of the recording and reading layers on which recording is performedby the first recording and reading optical system and ordinal positionsof the second set of the recording and reading layers on which recordingis performed by the second recording and reading optical systemcorrespond to each other, wherein the ordinal positions of the first setof the recording and reading layers are in order from closest to theside of the first surface, and the ordinal positions of the second setof the recording and reading layers are in order from closest to acenter of a thickness of the optical recording medium.
 62. The opticalrecording and reading apparatus according to claim 59, furthercomprising an output controller that, when information is recordedsimultaneously in the first set and the second set of the recording andreading layers by the first recording and reading optical system and thesecond recording and reading optical system, performs trial writing bythe first or second recording and reading beam on a trial writing areaof either the first set or the second set of the recording and readinglayers, to set optimum recording powers for both the first and secondrecording and reading beams.
 63. The optical recording and readingapparatus according to claim 59, further comprising an output controllerthat determines optimum recording powers of the first and secondrecording and reading beams and stores the optimum recording powers in amemory, wherein when an optimum recording power of the first recordingand reading beam for recording in an n-th recording and reading layer ofthe first set of the recording and reading layers in order from closestto a center of a thickness of the optical recording medium has beenundetermined and is to be set, if an optimum recording power of thesecond recording and reading beam for recording in an n-th recording andreading layer of the second set of the recording and reading layers inorder from closest to the center of the thickness of the opticalrecording medium has already been stored with reference to the memory,the output controller determines the optimum recording power of thesecond recording and reading beam to be the optimum recording power ofthe first recording and reading beam, and if the optimum recording powerof the second recording and reading beam for recording in the n-threcording and reading layer of the second set of the recording andreading layers has not been stored, the output controller performs trialwriting by the first recording and reading beam on a trial writing areaof the n-th recording and reading layer of the first set of therecording and reading layers to determine the optimum recording power ofthe first recording and reading beam, and stores the optimum recordingpower in the memory, and wherein when an optimum recording power of thesecond recording and reading beam for recording in an m-th recording andreading layer of the second set of the recording and reading layers inorder from closest to the center of the thickness of the opticalrecording medium has been undetermined and is to be set, if an optimumrecording power of the first recording and reading beam for recording inan m-th recording and reading layer of the first set of the recordingand reading layers in order from closest to the center of the thicknessof the optical recording medium has already been stored with referenceto the memory, the output controller determines the optimum recordingpower of the first recording and reading beam to be the optimumrecording power of the second recording and reading beam, and if theoptimum recording power of the first recording and reading beam forrecording in the m-th recording and reading layer of the first set ofthe recording and reading layers has not been stored, the outputcontroller performs trial writing by the second recording and readingbeam on a trial writing area of the m-th recording and reading layer ofthe second set of the recording and reading layers to determine theoptimum recording power of the second recording and reading beam, andstores the optimum recording power in the memory.
 64. The opticalrecording and reading apparatus according to claim 58, wherein theoptical recording medium has a substrate, and a plurality of therecording and reading layers are arranged on a side of the servo layerwith respect to the substrate, the recording and reading apparatusfurther comprising: a tracking optical system that applies a trackingbeam to the servo layer; a first recording and reading optical systemthat records information by applying a first recording and reading beamto a first recording and reading layer while tracking control using thetracking optical system is performed; and a second recording and readingoptical system that records information by applying a second recordingand reading beam to a second recording and reading layer while trackingcontrol using the tracking optical system is performed.
 65. The opticalrecording and reading apparatus according to claim 64, wherein thetracking optical system and the first recording and reading opticalsystem are arranged on a side of a first surface of the opticalrecording medium, and wherein the second recording and reading opticalsystem is arranged on a side of a second surface opposite to the firstsurface of the optical recording medium.
 66. The optical recording andreading apparatus according to claim 64, further comprising: a firstlinear motion mechanism that moves both the first recording and readingoptical system and the tracking optical system in tracking direction;and a second linear motion mechanism that moves the second recording andreading optical system in tracking direction, wherein the second linearmotion mechanism is controlled using a tracking signal of the trackingoptical system.
 67. The optical recording and reading apparatusaccording to claim 58, wherein the optical recording medium has a firstset of a plurality of the recording and reading layers between a firstsurface of the optical recording medium and the servo layer, and asecond set of a plurality of the recording and reading layers between asecond surface of the optical recording medium and the servo layer, theoptical recording and reading apparatus further comprising: a trackingoptical system that applies a tracking beam to the servo layer; a firstrecording and reading optical system that records information in a firstrotation direction as viewed from the first surface by applying a firstrecording and reading beam through the first surface to the firstrecording and reading layer while tracking control using the trackingoptical system is performed; and a second recording and reading opticalsystem that records information in a second rotation direction oppositeto the first rotation direction as viewed from the second surface byapplying a second recording and reading beam through the second surfaceto the second recording and reading layer while tracking control usingthe tracking optical system is performed, wherein the second recordingand reading optical system performs the recording simultaneously withthe recording which the first recording and reading optical systemperforms.
 68. The optical recording and reading apparatus according toclaim 67, further comprising: a first linear motion mechanism that movesboth the first recording and reading optical system and the trackingoptical system in tracking direction; and a second linear motionmechanism that moves the second recording and reading optical system intracking direction, wherein the second linear motion mechanism iscontrolled using a tracking signal of the tracking optical system. 69.The optical recording and reading apparatus according to claim 67,further comprising a digital signal processor that divides data to berecorded in the optical recording medium into first data to be recordedin the first recording and reading layer by the first recording andreading optical system and second data to be recorded in the secondrecording and reading layer by the second recording and reading opticalsystem.
 70. An optical recording medium comprising a servo layer havinga concavo-convex pattern or a groove for tracking control and arecording and reading layer having no concavo-convex pattern fortracking control, the recording and reading layer being previouslystacked or formed afterward, wherein information is recorded or read byapplying a recording and reading beam to the recording and reading layerwhile applying a tracking beam to the servo layer to perform trackingcontrol.
 71. The optical recording medium according to claim 70, whereininformation is recorded or read by applying a recording and reading beamhaving a second wavelength shorter than a first wavelength to therecording and reading layer while applying a tracking beam having thefirst wavelength to the servo layer to perform tracking control, andwherein a reflectance of the servo layer at a time when light of therecording and reading beam having the second wavelength is appliedthrough the recording and reading layer to the servo layer is lower thana reflectance of the servo layer at a time when light of the trackingbeam having the first wavelength is applied through the recording andreading layer to the servo layer.
 72. The optical recording mediumaccording to claim 71, wherein an amount of reflected light from theservo layer at a time when the recording and reading beam is appliedthrough the recording and reading layer to the servo layer is less thanor equal to five times of an amount of reflected light from therecording and reading layer at a time when the recording and readingbeam is applied to the recording and reading layer.
 73. The opticalrecording medium according to claim 71, wherein an amount of reflectedlight from the servo layer at a time when the recording and reading beamis applied through the recording and reading layer to the servo layer isless than an amount of reflected light from the recording and readinglayer at a time when the recording and reading beam is applied to therecording and reading layer.
 74. The optical recording medium accordingto claim 71, wherein an inter-layer distance between the recording andreading layer and the servo layer is 10 to 200 μm.
 75. The opticalrecording medium according to claim 71, wherein the reflectance of theservo layer at a time when the tracking beam is applied through therecording and reading layer to the servo layer is 40% to 95%, and thereflectance of the servo layer at a time when the recording and readingbeam is applied through the recording and reading layer to the servolayer by way of experiment is less than or equal to 60%.
 76. The opticalrecording medium according to claim 71, wherein the servo layer has areflecting film that contains metal as a major component, and anauxiliary film that is arranged adjacent to the reflecting film and isdifferent in reflectance from the reflecting film.
 77. The opticalrecording medium according to claim 76, wherein the servo layer has thereflecting films the number of which is two or more, and the auxiliaryfilms the number of which is three or more.
 78. The optical recordingmedium according to claim 71, wherein a filter layer in which dye isbound or dispersed is provided between the servo layer and the recordingand reading layer, and wherein the filter layer has a low absorbance forthe first wavelength of the tracking beam, and a high absorbance for thesecond wavelength of the recording and reading beam.
 79. The opticalrecording medium according to claim 71, comprising the recording andreading layer as a first recording and reading layer, and furthercomprising a second recording and reading layer having no concavo-convexpattern for tracking control and being previously stacked or formedafterward on a side opposite to the first recording and reading layerwith respect to the servo layer, wherein information is recorded in thesecond recording and reading layer while tracking control is performedusing the servo layer.
 80. The optical recording medium according toclaim 79, wherein the servo layer is formed directly on a side of thefirst recording and reading layer with respect to a substrate, andwherein the second recording and reading layer is formed on a sideopposite to the servo layer with respect to the substrate.
 81. Theoptical recording medium according to claim 80, wherein the substrate ismade of a light transmitting material.
 82. The optical recording mediumaccording to claim 80, wherein the first recording and reading layer andthe second recording and reading layer are previously stacked or formedafterward in symmetrical positions with respect to a center of athickness of the substrate.
 83. The optical recording medium accordingto claim 80, wherein the thickness of the substrate is 10 to 600 μm. 84.The optical recording medium according to claim 70, further comprising asubstrate, wherein the servo layer is formed on one face of thesubstrate, wherein a first recording and reading layer is arranged on aside of the servo layer of the substrate, and a second recording andreading layer is arranged on a side opposite to the servo layer of thesubstrate, and wherein information is recorded in the first recordingand reading layer and the second recording and reading layer whiletracking control is performed using the servo layer.
 85. The opticalrecording medium according to claim 84, wherein the substrate is made ofa light transmitting material.
 86. The optical recording mediumaccording to claim 84, wherein a first buffer layer is stacked betweenthe first recording and reading layer that has been previously stackedand the servo layer, and a second buffer layer is stacked between thesecond recording and reading layer that has been previously stacked andthe substrate, wherein a thickness of the first buffer layer and athickness of the second buffer layer are substantially equal to eachother.
 87. The optical recording medium according to claim 86, whereinat a wavelength of the tracking beam applied to the servo layer, arefractive index of the substrate is higher than a refractive index ofthe second buffer layer.
 88. The optical recording medium according toclaim 86, wherein at a wavelength of the tracking beam applied to theservo layer, a refractive index of the substrate is higher than arefractive index of the first buffer layer.
 89. The optical recordingmedium according to claim 84, wherein the first recording and readinglayer and the second recording and reading layer are previously stackedor formed afterward in symmetrical positions with respect to a center ofa thickness of the substrate.
 90. The optical recording medium accordingto claim 84, wherein the first recording and reading layer comprises aplurality of the recording and reading layers, and the second recordingand reading layer comprises a plurality of the recording and readinglayers.
 91. The optical recording medium according to claim 84, whereina first cover layer is stacked outside the first recording and readinglayer that is farthest from the substrate, and a second cover layer isstacked outside the second recording and reading layer that is farthestfrom the substrate, and wherein a thickness of the first cover layer isset to be larger by a thickness of the substrate than a thickness of thesecond cover layer.
 92. The optical recording medium according to claim84, wherein the tracking beam applied to the servo layer is set to belonger in wavelength than the recording and reading beam applied to thefirst or the second recording and reading layer, and wherein areflectance of the servo layer in a case where the tracking beam isapplied is greater than a reflectance of the servo layer in a case wherethe recording and reading beam is applied to the servo layer by way ofexperiment.
 93. The optical recording medium according to claim 84,wherein a thickness of the substrate is 10 to 600 μm.
 94. The opticalrecording medium according to claim 70, comprising, as the servo layer:a first servo layer having a concavo-convex pattern or a groove for thetracking control in a first spiral direction; and a second servo layerhaving a concavo-convex pattern or a groove for the tracking control ina second spiral direction opposite to the first spiral direction,wherein a first set of a plurality of the recording and reading layersare arranged on a side of a first surface of the optical recordingmedium with respect to the first and second servo layers, and wherein asecond set of a plurality of the recording and reading layers arearranged on a side of a second surface of the optical recording mediumwith respect to the first and second servo layers.
 95. A method ofmanufacturing an optical recording medium, the method comprising thesteps of: forming a servo layer having a concavo-convex pattern or agroove for tracking control on one face of a substrate made of a lighttransmitting material; simultaneously stacking a first buffer layer tobe arranged on a side of the servo layer of the substrate and a secondbuffer layer to be arranged on a side opposite to the servo layer of thesubstrate; and simultaneously stacking a first recording and readinglayer to be arranged on a side of the first buffer layer and a secondrecording and reading layer to be arranged on a side of the secondbuffer layer, wherein the first recording and reading layer has a planerstructure with no concavo-convex pattern for tracking control, and thesecond recording and reading layer has a planer structure with noconcavo-convex pattern for tracking control.
 96. The method ofmanufacturing an optical recording medium according to claim 95, furthercomprising the step of stacking a first cover layer to be arranged on aside of the first recording and reading layer and a second cover layerto be arranged on a side of the second recording and reading layerseparately from each other.